CN111684801A - Bidirectional intra prediction method and device - Google Patents

Abstract

A video decoding method and apparatus and a video encoding method and apparatus are disclosed. The encoding and decoding of the target block are performed using intra prediction. The intra prediction is bidirectional intra prediction and is intra prediction using the remaining mode. In bidirectional intra prediction, a prediction value of a target pixel in a target block is determined based on reference pixels in two directions according to bidirectional intra prediction. In the intra prediction using the remaining modes, the remaining modes are the remaining intra prediction modes except for the MPMs in the MPM list.

Description

Bidirectional intra prediction method and device

technical field

The following embodiments generally relate to a video decoding method and apparatus and a video encoding method and apparatus, and more particularly, to a video decoding method and apparatus and a video encoding method and apparatus using bidirectional intra prediction.

Background technique

With the continuous development of the information and communication industry, broadcasting services supporting high definition (HD) resolution have become widespread throughout the world. Through this popularity, a large number of users have become accustomed to high-resolution and high-definition images and/or videos.

In order to meet users' demands for high definition, a large number of institutions have accelerated the development of next-generation imaging devices. In addition to high definition TV (HDTV) and full high definition (FHD) TV, user interest in UHD TV has also increased, wherein the resolution of UHD TV is more than four times that of full high definition (FHD) TV. As its interest increases, there is a constant need for image encoding/decoding techniques for images with higher resolution and higher definition.

The image encoding/decoding apparatus and method may use an inter-frame prediction technique, an intra-frame prediction technique, an entropy encoding technique, etc., in order to perform encoding/decoding on high-resolution and high-definition images. The inter prediction technique may be a technique for predicting values of pixels included in a target picture using a temporally preceding picture and/or a temporally succeeding picture. The intra prediction technique may be a technique for predicting values of pixels included in a target picture using information about pixels in the target picture. Entropy coding techniques may be techniques for assigning short codewords to frequently occurring symbols and long codewords to infrequently occurring symbols.

In intra prediction, various detailed techniques have been developed, and due to the application of these detailed techniques, the accuracy and efficiency of prediction can be improved.

SUMMARY OF THE INVENTION

technical problem

Embodiments aim to provide an encoding apparatus and method and a decoding apparatus and method using bidirectional intra prediction.

The embodiments aim to provide an encoding apparatus and method and a decoding apparatus and method using the residual mode.

Technical solutions

According to an aspect, there is provided a decoding method comprising: determining an intra prediction mode to be applied to decoding of a target block; and performing intra prediction for the target block using the determined intra prediction mode, wherein the The intra prediction mode is a bidirectional intra prediction mode, and wherein the intra prediction is bidirectional intra prediction.

The bidirectional intra prediction mode may be determined based on the availability of pixels in neighboring blocks located in the specified direction of the target block.

The bidirectional intra prediction mode may be determined based on prediction modes of neighboring blocks of the target block.

The two directions of bidirectional intra prediction may be two opposite linear directions.

Virtual neighboring pixels may be generated in a specified direction of the target block, and bidirectional intra prediction may be performed for the target block using the virtual neighboring pixels.

The specified direction may be one or more of a right direction and a downward direction.

A predicted value for a target pixel in a target block may be derived using pixels in adjacent blocks in both directions of bidirectional intra prediction.

The predicted value for the target pixel may be derived using a weight according to the distance between each pixel in the adjacent block and the target pixel in the target block located in both directions of the bidirectional intra prediction.

A prediction value for a target pixel in a target block may be derived using weights for both directions of bidirectional intra prediction.

A unidirectional/bidirectional classification indicator and an intra prediction mode indicator may be used to determine whether the bidirectional intra prediction mode for the target block is to be used.

The two directions of bidirectional intra prediction may be determined based on the two directions indicated by the two intra prediction mode indicators.

A single intra prediction mode indicator may indicate one of the direction of unidirectional intra prediction and the direction of bidirectional intra prediction.

One of unidirectional intra prediction and bidirectional intra prediction may be selected according to the availability of reference pixels in a direction corresponding to the direction indicated by the intra prediction mode indicator.

It may be determined which of unidirectional intra prediction and bidirectional intra prediction will be used for the entire target block.

It may be determined which of unidirectional intra prediction and bidirectional intra prediction will be used for each of the pixels in the target block.

For the first and second directions of bidirectional intra prediction, when either the reference pixel in the first direction or the reference pixel in the second direction is unavailable, padding may be used to generate the value of the unavailable reference pixel.

The prediction value for the target pixel in the target block may be determined using at least one of the reference pixels located in the two prediction directions of the bidirectional intra prediction mode.

A weight can be applied to each of the reference pixels.

The remaining mode indicator may indicate a remaining mode to be used for intra prediction of the target block among the plurality of remaining modes.

The plurality of remaining modes may be remaining intra-prediction modes other than the MPM present in the most probable mode (MPM) list.

The intra prediction mode may be determined based on a number of different lists.

According to another aspect, there is provided an encoding method comprising: determining an intra prediction mode to be applied to decoding of a target block; and performing intra prediction for the target block using the determined intra prediction mode, wherein, The intra prediction mode is a bidirectional intra prediction mode, and wherein the intra prediction is bidirectional intra prediction.

According to another aspect, there is provided a computer-readable storage medium storing a bitstream for image decoding, the bitstream including information about an encoded target block, wherein the decoded frame to be applied to the target block An intra-prediction mode is determined, and wherein, intra-prediction for the target block using the information on the encoded target block and the determined intra-prediction mode is performed.

beneficial effect

An encoding apparatus and method and a decoding apparatus and method using bidirectional intra prediction are provided.

Provided are an encoding apparatus and method using a residual mode and a decoding apparatus and method.

Description of drawings

1 is a block diagram showing the configuration of an embodiment of an encoding apparatus to which the present disclosure is applied;

2 is a block diagram showing a configuration of an embodiment of a decoding apparatus to which the present disclosure is applied;

3 is a diagram schematically showing a partition structure of an image when the image is encoded and decoded;

4 is a diagram illustrating a form of a prediction unit (PU) that a coding unit (CU) can include;

5 is a diagram illustrating the form of a transform unit (TU) that can be included in a CU;

Figure 6 shows the division of blocks according to an example;

7 is a diagram for explaining an embodiment of an intra prediction process;

8 is a diagram for explaining the positions of reference samples used in the intra prediction process;

9 is a diagram for explaining an embodiment of an inter prediction process;

Figure 10 illustrates a spatial candidate according to an embodiment;

11 illustrates the order of adding motion information of spatial candidates to a merge list, according to an embodiment;

Figure 12 illustrates transform and quantization processing according to an example;

Figure 13 shows a diagonal scan according to an example;

Figure 14 shows a horizontal scan according to an example;

Figure 15 shows vertical scanning according to an example;

16 is a configuration diagram of an encoding apparatus according to an embodiment;

17 is a configuration diagram of a decoding apparatus according to an embodiment;

18 is a flowchart of a bidirectional intra prediction method according to an embodiment;

19 illustrates a unidirectional intra prediction mode according to an example;

20 illustrates a bidirectional intra prediction mode according to an example;

21 illustrates a bidirectional intra prediction mode using virtual neighboring pixels, according to an example;

22 illustrates the derivation and selection of bidirectional intra prediction from the direction of an intra prediction mode indicator, according to an example;

23 illustrates the generation of virtual neighboring pixels according to an example;

24 illustrates the use of virtual neighboring pixels to generate additional virtual neighboring pixels, according to an example;

25 illustrates the generation of lower right virtual neighbors and middle virtual neighbors, according to an example;

26 illustrates bidirectional intra prediction according to an example;

27 illustrates bidirectional intra prediction using virtual neighboring pixels, according to an example;

28 illustrates bidirectional intra prediction using distances between neighboring pixels and target pixels, according to an example;

29 illustrates bidirectional intra prediction using distances between virtual neighboring pixels and target pixels, according to an example;

30 illustrates the use of residual modes to determine intra-prediction modes, according to an embodiment;

31 illustrates deriving MPM after determining whether MPM is used and using remaining modes to determine intra prediction mode, according to an embodiment;

32 illustrates blocks for deriving MPM candidates, according to an example;

33 illustrates binarization of residual mode indicators according to an example;

34 is a flowchart of a target block prediction method and a bitstream generation method according to an embodiment; and

FIG. 35 is a flowchart of a target block prediction method using a bitstream according to an embodiment.

Detailed ways

The present invention may be variously modified and may have various embodiments, and specific embodiments will be described in detail below with reference to the accompanying drawings. It should be understood, however, that these examples are not intended to limit the invention to the particular disclosed forms, and that they include all changes, equivalents, or modifications included within the spirit and scope of the invention.

The following exemplary embodiments will be described in detail with reference to the accompanying drawings that illustrate specific embodiments. These embodiments are described so that those of ordinary skill in the art to which this disclosure pertains can easily practice the embodiments. It should be noted that the various embodiments differ from each other, but need not be mutually exclusive. For example, the specific shapes, structures, and characteristics described herein can be implemented in other embodiments without departing from the spirit and scope of the various embodiments associated with one embodiment. Furthermore, it is to be understood that the location or arrangement of the various components in each disclosed embodiment can be changed without departing from the spirit and scope of the embodiments. Therefore, the appended detailed description is not intended to limit the scope of the present disclosure, and the scope of the exemplary embodiments is limited only by the appended claims and their equivalents, so long as they are properly described.

In the drawings, like reference numerals are used to designate the same or similar functions in various respects. The shapes, sizes, etc. of components in the drawings may be exaggerated for clarity of description.

Terms such as "first" and "second" may be used to describe various components, but the components are not limited by the terms. The terms are only used to distinguish one component from another. For example, a first component could be termed a second component without departing from the scope of this specification. Similarly, the second component may be referred to as the first component. The term "and/or" can include a combination of multiple associated descriptive items or any one of the multiple associated descriptive items.

It will be understood that when a component is referred to as being "connected" or "coupled" to another component, the two components can be directly connected or coupled to each other or intervening components may be present between the two components. It will be understood that when components are referred to as being "directly connected or coupled," there are no intervening components between the two components.

Furthermore, the components described in the embodiments are shown independently to represent different feature functions, but this does not mean that each component is formed by a separate piece of hardware or software. That is, for convenience of description, a plurality of components are individually arranged and included. For example, at least two of the plurality of components may be integrated into a single component. Conversely, a component can be divided into multiple components. Embodiments in which a plurality of components are integrated or embodiments in which some components are separated are included in the scope of the present specification as long as they do not depart from the essence of the present specification.

Furthermore, it should be noted that, in an exemplary embodiment, the expression describing that a component "includes" a particular component means that additional components may be included within the scope of the practical or technical spirit of the exemplary embodiment, but does not preclude the existence of Components other than a specific component.

The terms used in this specification are used to describe specific embodiments only, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context specifically indicates the contrary. In this specification, it should be understood that terms such as "comprising" or "having" are only intended to indicate the presence of features, numbers, steps, operations, components, parts or combinations thereof, and are not intended to preclude the presence or addition of one or more the possibility of other features, numbers, steps, operations, components, parts or combinations thereof.

The embodiments will be described in detail below with reference to the accompanying drawings so that those skilled in the art to which the embodiments pertain can easily practice the embodiments. In the following description of the embodiments, detailed descriptions of well-known functions or configurations that are considered to obscure the gist of the present specification will be omitted. Also, the same reference numerals are used throughout the drawings to designate the same components, and repeated descriptions of the same components will be omitted.

Hereinafter, "image" may refer to a single picture that constitutes a video, or may refer to the video itself. For example, "encoding and/or decoding an image" may mean "encoding and/or decoding a video", and may also mean "encoding and/or decoding any one of a plurality of images constituting a video".

Hereinafter, the terms "video" and "moving picture" may be used to have the same meaning and may be used interchangeably with each other.

Hereinafter, the target image may be an encoding target image that is a target to be encoded and/or a decoding target image that is a target to be decoded. Also, the target image may be an input image input to an encoding device or an input image input to a decoding device.

Hereinafter, the terms "image", "picture", "frame" and "screen" may be used to have the same meaning and may be used interchangeably with each other.

Hereinafter, the target block may be an encoding target block (ie, a target to be encoded) and/or a decoding target block (ie, a target to be decoded). Furthermore, the target block may be the current block, ie the target currently to be encoded and/or decoded. Here, the terms "target block" and "current block" may be used to have the same meaning and may be used interchangeably with each other.

Hereinafter, the terms "block" and "unit" may be used to have the same meaning and may be used interchangeably with each other. Alternatively, a "block" may refer to a specific unit.

In the following, the terms "region" and "section" are used interchangeably with each other.

Hereinafter, the specific signal may be a signal indicating a specific block. For example, the original signal may be a signal indicating the target block. The prediction signal may be a signal indicating a prediction block. The residual signal may be a signal indicative of a residual block.

In the following embodiments, certain information, data, flags, elements and attributes may have their respective values. A value of "0" corresponding to each of the information, data, flags, elements and attributes may indicate a logical false or a first predefined value. In other words, the value "0", false, logical false and the first predefined value can be used interchangeably with each other. A value of "1" corresponding to each of the information, data, flags, elements and attributes may indicate logical true or a second predefined value. In other words, the value "1", true, logical true and the second predefined value can be used interchangeably with each other.

When a variable such as i or j is used to indicate a row, column, or index, the value i may be an integer of 0 or greater, or an integer of 1 or greater. In other words, in an embodiment, each of the row, column, and index may be counted from 0, or may be counted from 1.

Hereinafter, terms to be used in the embodiments will be described.

Encoder: An encoder represents a device for performing encoding.

Decoder: A decoder represents a device for performing decoding.

Unit: A "unit" may represent a unit of image encoding and decoding. The terms "unit" and "block" may be used to have the same meaning and may be used interchangeably with each other.

– A "cell" can be an array of MxN samples. M and N may each be a positive integer. The term "cell" may generally refer to a two-dimensional (2D) array of samples.

– During the encoding and decoding of images, a "unit" can be an area generated by partitioning an image. In other words, a "cell" can be a designated area in an image. A single image can be partitioned into multiple cells. Alternatively, a picture may be partitioned into sub-portions, and a unit may represent each partitioned sub-portion when encoding or decoding is performed on the partitioned sub-portions.

– During the encoding and decoding of images, pre-defined processing can be performed on each cell according to the cell type.

- Unit types can be classified into macrounits, coding units (CUs), prediction units (PUs), residual units, transform units (TUs), etc., according to function. Alternatively, depending on the function, a unit may represent a block, a macroblock, a coding tree unit, a coding tree block, a coding unit, a coding block, a prediction unit, a prediction block, a residual unit, a residual block, a transform unit, a transform block, or the like.

- The term "unit" may denote information including a luma component block, a chroma component block corresponding to the luma component block, and syntax elements for each block such that the unit is designated as distinct from the block.

- The size and shape of the cells can be implemented differently. Furthermore, the cells may have any of a variety of sizes and shapes. Specifically, the shape of the cells may include not only squares, but also geometrical shapes (such as rectangles, trapezoids, triangles, and pentagons) that can be represented in two dimensions (2D).

- Further, the unit information may include one or more of the type of the unit, the size of the unit, the depth of the unit, the encoding order of the unit, the decoding order of the unit, and the like. For example, the type of unit may indicate one of CU, PU, residual unit, and TU.

- A unit may be partitioned into subunits, each subunit having a smaller size than the size of the associated unit.

– Depth: Depth may represent the extent to which the cell is partitioned. Furthermore, the cell depth may indicate the level at which the corresponding cell exists when the cell is represented in a tree structure.

- The cell partition information may include a depth indicating the depth of the cell. The depth may indicate the number of times the cell is partitioned and/or the degree to which the cell is partitioned.

– In a tree structure, it can be considered that the depth of the root node is the smallest and the depth of the leaf nodes is the largest.

- A single unit can be hierarchically partitioned into multiple sub-units, while the single unit has depth information based on a tree structure. In other words, a unit and subunits generated by partitioning the unit may correspond to a node and a child node of the node, respectively. Each partitioned subunit may have a unit depth. Since the depth indicates the number of times the unit is partitioned and/or the degree to which the unit is partitioned, the partition information of a sub-unit may include information about the size of the sub-unit.

– In a tree structure, the top node may correspond to the initial node before partitioning. The top node may be referred to as the "root node". Also, the root node may have a minimum depth value. Here, the depth of the top node may be level "0".

- Nodes with a depth of level "1" may represent cells that were generated when the initial cell was partitioned once. Nodes with a depth of level "2" may represent cells that were generated when the original cell was partitioned twice.

- A leaf node with a depth of level "n" may represent a cell generated when the original cell is partitioned n times.

– Leaf nodes can be bottom nodes that cannot be further partitioned. The depth of a leaf node can be a maximum level. For example, the predefined value for the maximum level may be 3.

-QT depth may represent the depth for the quad partition. The BT depth may represent the depth for two partitions. TT depth may represent the depth for three partitions.

– Sample: A sample can be the basic unit that makes up a block. A sample can be represented by a value from 0 to 2 ^Bd -1 according to the bit depth (Bd).

– Samples can be pixels or pixel values.

- In the following, the terms "pixel" and "sample" may be used to have the same meaning and may be used interchangeably with each other.

Coding Tree Unit (CTU): A CTU may consist of a single luma component (Y) coding tree block and two chroma component (Cb, Cr) coding tree blocks associated with the luma component coding tree block. Also, the CTU may represent information including the above-described blocks and syntax elements for each block.

– Each coding tree unit (CTU) may be partitioned using one or more partitioning methods, such as quad-tree (QT), binary-tree (BT), and ternary-tree (TT), in order to configure subunits, such as coding units , prediction unit and transform unit.

- "CTU" may be used as a term to designate a block of pixels that is a processing unit in image decoding and encoding processes, such as in the case of partitioning an input image.

Coding Tree Block (CTB): "CTB" may be used as a term to designate any one of a Y coding tree block, a Cb coding tree block, and a Cr coding tree block.

Neighboring Blocks: Neighboring blocks (or neighboring blocks) may represent blocks that are adjacent to the target block. Neighboring blocks may represent reconstructed neighboring blocks.

Hereinafter, the terms "adjacent block" and "adjacent block" may be used to have the same meaning, and may be used interchangeably with each other.

Spatial Neighboring Block: A spatially neighboring block may be a block that is spatially adjacent to the target block. The adjacent blocks may include spatially adjacent blocks.

- The target block and spatially adjacent blocks may be included in the target picture.

- A spatially adjacent block may represent a block whose boundary is in contact with the target block or a block located within a predetermined distance from the target block.

- A spatially adjacent block may represent a block adjacent to a vertex of the target block. Here, the block adjacent to the vertex of the target block may represent a block that is vertically adjacent to a neighboring block that is horizontally adjacent to the target block or a block that is horizontally adjacent to a neighboring block that is vertically adjacent to the target block.

Temporal Neighboring Block: A temporally neighboring block may be a block that is temporally adjacent to the target block. The adjacent blocks may include temporally adjacent blocks.

- Temporally adjacent blocks may include co-located blocks (col blocks).

The -col block may be a block in a previously reconstructed co-located picture (col picture). The position of the col block in the col picture may correspond to the position of the target block in the target picture. Alternatively, the position of the col block in the col picture may be equal to the position of the target block in the target picture. The col picture may be a picture included in the reference picture list.

- A temporally adjacent block may be a block that is temporally adjacent to a spatially adjacent block of the target block.

Prediction unit: A prediction unit may be a basic unit for prediction such as inter prediction, intra prediction, inter compensation, intra compensation and motion compensation.

- A single prediction unit may be divided into multiple partitions or sub-prediction units of smaller size. The plurality of partitions may also be basic units when performing prediction or compensation. A partition generated by dividing a prediction unit may also be a prediction unit.

Prediction unit partition: A prediction unit partition may be the shape into which the prediction unit is divided.

Reconstructed Neighbors: Reconstructed neighbors may be units that have been decoded and reconstructed around the target unit.

- The reconstructed neighbor cells may be cells that are spatially adjacent to the target cell or temporally adjacent to the target cell.

- A reconstructed spatially adjacent unit may be a unit included in the target picture that has been reconstructed by encoding and/or decoding.

- A reconstructed temporally adjacent unit may be a unit included in the reference picture that has been reconstructed by encoding and/or decoding. The position of the reconstructed temporally adjacent unit in the reference image may be the same as the position of the target unit in the target picture, or may correspond to the position of the target unit in the target picture.

Parameter set: The parameter set can be header information in the structure of the bitstream. For example, parameter sets may include video parameter sets, sequential parameter sets, picture parameter sets, adaptive parameter sets, and the like.

Also, the parameter set may include slice header information and parallel block header information.

Rate-distortion optimization: An encoding device may use rate-distortion optimization in order to provide high encoding efficiency by utilizing a combination of: coding unit (CU) size, prediction mode, prediction unit (PU) size, motion information, and transform unit (TU) )size of.

- The rate-distortion optimization scheme can calculate the rate-distortion cost of each combination to select the optimal combination from these combinations. The rate-distortion penalty can be calculated using Equation 1 below. In general, the combination that minimizes the rate-distortion penalty can be selected as the optimal combination under the rate-distortion optimization scheme.

[Equation 1]

D+λ*R

-D for distortion. D may be the average of the squares of the differences between the original transform coefficients and the reconstructed transform coefficients in the transform unit (ie, the mean squared error).

-R may represent the rate, which may use relevant context information to represent the bit rate.

–λ represents the Lagrange multiplier. R may include not only encoding parameter information such as prediction mode, motion information, and encoding block flags, but also bits generated as a result of encoding transform coefficients.

- The encoding device may perform processes such as inter prediction and/or intra prediction, transform, quantization, entropy coding, inverse quantization (inverse quantization) and inverse transform in order to calculate exact D and R. These processes can greatly increase the complexity of the encoding device.

- Bitstream: A bitstream may represent a stream of bits comprising encoded image information.

- Parameter set: The parameter set may be header information in the structure of the bitstream.

The parameter set may include at least one of a video parameter set, an order parameter set, a picture parameter set, and an adaptive parameter set. Furthermore, the parameter set may include information on slice headers and information on parallel block headers.

Parsing: Parsing may be a decision on the value of a syntax element made by performing entropy decoding on the bitstream. Alternatively, the term "parse" may refer to this entropy decoding itself.

Symbol: A symbol may be at least one of a syntax element, an encoding parameter, and a transform coefficient of the encoding target unit and/or the decoding target unit. Furthermore, the symbols can be the target of entropy encoding or the result of entropy decoding.

Reference picture: A reference picture may be an image that is referenced by a unit in order to perform inter prediction or motion compensation. Alternatively, the reference picture may be a picture including a reference unit that is referenced by the target unit in order to perform inter prediction or motion compensation.

Hereinafter, the terms "reference picture" and "reference image" may be used to have the same meaning and may be used interchangeably with each other.

Reference picture list: The reference picture list may be a list including one or more reference pictures used for inter prediction or motion compensation.

- Types of reference picture lists may include merged list (LC), list 0 (L0), list 1 (L1), list 2 (L3), list 3 (L3), etc.

- For inter prediction, one or more reference picture lists may be used.

Inter prediction indicator: The inter prediction indicator may indicate the inter prediction direction for the target unit. Inter prediction may be one of unidirectional prediction and bidirectional prediction. Alternatively, the inter prediction indicator may represent the number of reference pictures used to generate the prediction unit of the target unit. Alternatively, the inter prediction indicator may represent the number of prediction blocks used for inter prediction or motion compensation of the target unit.

Reference picture index: The reference picture index may be an index indicating a specific reference picture in the reference picture list.

Motion Vector (MV): A motion vector can be a 2D vector used for inter prediction or motion compensation. The motion vector can represent the offset between the target image and the reference image.

- For example, the MV can be represented in a form such as (mv _x , mv _y ). mv _x may indicate the horizontal component and mv _y may indicate the vertical component.

- Search range: The search range may be the 2D area where the search for the MV is performed during inter prediction. For example, the size of the search range may be MxN. M and N may each be a positive integer.

Motion vector candidate: A motion vector candidate may be a block that is a prediction candidate when the motion vector is predicted or a motion vector of a block that is a prediction candidate.

- Motion vector candidates may be included in the motion vector candidate list.

Motion Vector Candidate List: A motion vector candidate list may be a list configured using one or more motion vector candidates.

Motion Vector Candidate Index: The motion vector candidate index may be an indicator for indicating a motion vector candidate in the motion vector candidate list. Alternatively, the motion vector candidate index may be an index of a motion vector predictor.

Motion information: The motion information may be information including at least one of a reference picture list, a reference picture, a motion vector candidate, a motion vector candidate index, a merge candidate, and a merge index, and a motion vector, a reference picture index, and an inter prediction indicator.

Merge candidate list: The merge candidate list may be a list using the merge candidate configuration.

Merging candidate: The merging candidate may be a spatial merging candidate, a temporal merging candidate, a combined merging candidate, a combined bi-predictive merging candidate, a zero merging candidate, and the like. Merge candidates may include motion information, such as prediction type information, reference picture indices for each list, and motion vectors.

Merge Index: The merge index may be an indicator for indicating a merge candidate in the merge candidate list.

- The merge index may indicate a reconstruction unit for deriving a merge candidate between a reconstruction unit that is spatially adjacent to the target unit and a reconstruction unit that is temporally adjacent to the target unit.

- The merge index may indicate at least one of multiple pieces of motion information of a merge candidate.

Transform unit: A transform unit may be a basic unit for residual signal encoding and/or residual signal decoding, such as transform, inverse transform, quantization, inverse quantization, transform coefficient encoding, and transform coefficient decoding. A single transform unit may be partitioned into multiple transform units with smaller sizes.

Scaling: Scaling can refer to the process of multiplying a factor by a transform coefficient level.

- Transform coefficients may be generated as a result of scaling transform coefficient levels. Scaling may also be referred to as "inverse quantization".

Quantization parameter (QP): A quantization parameter may be a value used to generate transform coefficient levels for transform coefficients in quantization. Optionally, the quantization parameter may also be a value used to generate transform coefficients by scaling transform coefficient levels in inverse quantization. Alternatively, the quantization parameter may be a value mapped to a quantization step size.

Delta quantization parameter: The delta quantization parameter is the difference between the quantization parameter of the target unit and the predicted quantization parameter.

Scanning: Scanning can represent a method of arranging the order of coefficients in a cell, block, or matrix. For example, a method for arranging a 2D array in the form of a one-dimensional (1D) array may be referred to as "scanning". Alternatively, the method for arranging a 1D array in the form of a 2D array may also be referred to as "scanning" or "inverse scanning".

Transform coefficients: Transform coefficients may be coefficient values generated when an encoding device performs transform. Alternatively, the transform coefficients may be coefficient values generated when the decoding apparatus performs at least one of entropy decoding and inverse quantization.

- Quantized levels or quantized transform coefficient levels generated by applying quantization to transform coefficients or residual signals may also be included in the meaning of the term "transform coefficients".

Level of quantization: The level of quantization may be a value generated when an encoding apparatus performs quantization on a transform coefficient or residual signal. Alternatively, the level of quantization may be a value that is a target of inverse quantization when the decoding apparatus performs inverse quantization.

- Quantized transform coefficient levels that are the result of transform and quantization may also be included in the meaning of quantized levels.

Non-zero transform coefficients: Non-zero transform coefficients may be transform coefficients having values other than zero, or may be transform coefficient levels having values other than zero. Alternatively, the non-zero transform coefficients may be transform coefficients whose magnitudes are not zero, or may be transform coefficient levels whose magnitudes are not zero.

Quantization matrix: A quantization matrix can be a matrix used in the quantization process or inverse quantization process in order to improve the subjective image quality or objective image quality of an image. The quantization matrix may also be referred to as a "scale list".

Quantization matrix coefficients: The quantization matrix coefficients can be each element in the quantization matrix. The quantization matrix coefficients may also be referred to as "matrix coefficients".

Default matrix: The default matrix can be a quantization matrix pre-defined by the encoding device and the decoding device.

Non-default matrix: The non-default matrix may be a quantization matrix that is not predefined by the encoding device and the decoding device. The non-default matrix may be signaled by the encoding device to the decoding device.

Most Probable Mode (MPM): MPM may represent an intra prediction mode that is used for intra prediction for a target block with a high probability.

The encoding apparatus and the decoding apparatus may determine one or more MPMs based on encoding parameters related to the target block and attributes of objects related to the target block.

The encoding apparatus and the decoding apparatus may determine one or more MPMs based on the intra prediction mode of the reference block. A reference block may include multiple reference blocks. The plurality of reference blocks may include a spatially adjacent block adjacent to the left of the target block and a spatially adjacent block adjacent to the upper side of the target block. In other words, one or more different MPMs may be determined depending on which intra prediction modes have been used for the reference block.

One or more MPMs may be determined in the same manner in both the encoding device and the decoding device. That is, the encoding apparatus and the decoding apparatus may share the same MPM list including one or more MPMs.

MPM list: An MPM list can be a list that includes one or more MPMs. The number of one or more MPMs in the MPM list may be predefined.

MPM indicator: The MPM indicator may indicate an MPM among one or more MPMs in the MPM list to be used for intra prediction for the target block. For example, the MPM indicator may be an index for the MPM list.

Since the MPM list is determined in the same way in both the encoding device and the decoding device, it may not be necessary to send the MPM list itself from the encoding device to the decoding device.

The MPM indicator may be signaled from the encoding device to the decoding device. Since the MPM indicator is signaled, the decoding apparatus may determine the MPM to be used for intra prediction for the target block among the MPMs in the MPM list.

MPM usage indicator: The MPM usage indicator may indicate whether the MPM usage mode is to be used for prediction for the target block. The MPM usage mode may be a mode in which the MPM to be used for intra prediction for the target block is determined using the MPM list.

The MPM usage indicator may be signaled from the encoding device to the decoding device.

Signaling: "Signaling" may mean that information is sent from an encoding device to a decoding device. Alternatively, the signaling may indicate that the information is included in the bitstream or storage medium. The information signaled by the encoding device can be used by the decoding device.

FIG. 1 is a block diagram showing the configuration of an embodiment of an encoding apparatus to which the present disclosure is applied.

The encoding device 100 may be an encoder, a video encoding device, or an image encoding device. A video may include one or more images (pictures). The encoding apparatus 100 may sequentially encode one or more pictures of the video.

1, the encoding apparatus 100 includes an inter prediction unit 110, an intra prediction unit 120, a switch 115, a subtractor 125, a transform unit 130, a quantization unit 140, an entropy encoding unit 150, an inverse quantization (inverse quantization) unit 160, Inverse transform unit 170 , adder 175 , filter unit 180 and reference picture buffer 190 .

The encoding apparatus 100 may perform encoding on the target image using the intra mode and/or the inter mode.

Also, the encoding apparatus 100 may generate a bitstream including information on encoding by encoding the target image, and may output the generated bitstream. The generated bitstream can be stored in a computer-readable storage medium, and can be streamed over a wireless/wired transmission medium.

When the intra mode is used as the prediction mode, the switch 115 may switch to the intra mode. When the inter mode is used as the prediction mode, the switcher 115 may switch to the inter mode.

The encoding apparatus 100 may generate a prediction block of the target block. Also, after the prediction block has been generated, the encoding apparatus 100 may encode the residual between the target block and the prediction block.

When the prediction mode is the intra mode, the intra prediction unit 120 may use the pixels of the previously encoded/decoded neighboring blocks around the target block as reference samples. Intra-prediction unit 120 may perform spatial prediction on the target block using the reference samples, and may generate prediction samples for the target block via spatial prediction.

The inter prediction unit 110 may include a motion prediction unit and a motion compensation unit.

When the prediction mode is inter mode, the motion prediction unit may search a reference image for a region that best matches the target block in the motion prediction process, and may derive a motion vector for the target block and the found region based on the found region.

Reference images may be stored in the reference picture buffer 190 . More specifically, the reference picture may be stored in the reference picture buffer 190 when encoding and/or decoding of the reference picture has been processed.

The motion compensation unit may generate a prediction block for the target block by performing motion compensation using the motion vector. Here, the motion vector may be a two-dimensional (2D) vector used for inter prediction. Furthermore, the motion vector may represent the offset between the target image and the reference image.

When the motion vector has a value other than an integer, the motion prediction unit and the motion compensation unit may generate a prediction block by applying an interpolation filter to a partial region of the reference image. In order to perform inter prediction or motion compensation, it may be determined which of skip mode, merge mode, advanced motion vector prediction (AMVP) mode, and current picture reference mode corresponds to a CU-based PU for PUs included in the CU A method of predicting and compensating for motion, and inter-prediction or motion compensation may be performed according to this mode.

Subtractor 125 may generate a residual block, where the residual block is the difference between the target block and the prediction block. The residual block may also be referred to as a "residual signal".

The residual signal may be the difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming or quantizing the difference between the original signal and the predicted signal or a signal generated by transforming and quantizing the difference. The residual block may be a residual signal for block units.

The transform unit 130 may generate transform coefficients by transforming the residual block, and may output the generated transform coefficients. Here, the transform coefficients may be coefficient values generated by transforming the residual block.

Transform unit 130 may use one of a number of predefined transform methods when performing the transform.

A number of predefined transform methods may include discrete cosine transform (DCT), discrete sine transform (DST), Karhunen-Loeve transform (KLT), and the like.

A transform method for transforming the residual block may be determined according to at least one of encoding parameters for the target block and/or neighboring blocks. For example, the transform method may be determined based on at least one of the inter prediction mode for the PU, the intra prediction mode for the PU, the size of the TU, and the shape of the TU. Alternatively, transform information indicating the transform method may be signaled from the encoding apparatus 100 to the decoding apparatus 200 .

When transform skip mode is used, transform unit 130 may omit transforming the residual block.

By quantizing the transform coefficients, a quantized transform coefficient level or a quantized level can be generated. Hereinafter, in an embodiment, each of the quantized transform coefficient level and the quantized level may also be referred to as a "transform coefficient".

The quantization unit 140 may generate a quantized transform coefficient level or a quantized level by quantizing the transform coefficient according to the quantization parameter. The quantization unit 140 may output the generated quantized transform coefficient level or quantized level. In this case, the quantization unit 140 may quantize the transform coefficients using a quantization matrix.

The entropy encoding unit 150 may generate a bitstream by performing probability distribution-based entropy encoding based on values calculated by the quantization unit 140 and/or encoding parameter values calculated during encoding. The entropy encoding unit 150 may output the generated bitstream.

The entropy encoding unit 150 may perform entropy encoding on information about pixels of the image and information required to decode the image. For example, information required to decode an image may include syntax elements and the like.

When entropy coding is applied, fewer bits can be allocated to more frequently occurring symbols, and more bits can be allocated to infrequently occurring symbols. Since the symbols are represented by this allocation, the size of the bit string for the target symbol to be encoded can be reduced. Therefore, the compression performance of video coding can be improved by entropy coding.

Also, for entropy encoding, the entropy encoding unit 150 may use an encoding method such as Exponential Golomb, Context Adaptive Variable Length Coding (CAVLC), or Context Adaptive Binary Arithmetic Coding (CABAC). For example, the entropy encoding unit 150 may perform entropy encoding using a variable length coding/code (VLC) table. For example, entropy encoding unit 150 may derive a binarization method for the target symbol. Additionally, entropy encoding unit 150 may derive a probability model for the target symbol/bin. The entropy encoding unit 150 may perform arithmetic encoding using the derived binarization method, probability model, and context model.

The entropy encoding unit 150 may transform coefficients in a 2D block form into a 1D vector form through a transform coefficient scanning method in order to encode the quantized transform coefficient levels.

Encoding parameters may be information required for encoding and/or decoding. The encoding parameters may include information encoded by the encoding apparatus 100 and transmitted from the encoding apparatus 100 to the decoding apparatus, and may also include information that may be derived during encoding or decoding. For example, the information sent to the decoding device may include syntax elements.

Encoding parameters may include not only information such as syntax elements (or flags or indices) encoded by the encoding device and signaled by the encoding device to the decoding device, but also information derived in the encoding or decoding process. Furthermore, the encoding parameters may include information required to encode or decode the image. For example, the coding parameters may include at least one of the following values, a combination or statistics of: size of unit/block, depth of unit/block, partition information of unit/block, partition structure of unit/block, indicating unit/block Information whether the block is partitioned in a quad-tree structure, information indicating whether the unit/block is partitioned in a binary tree structure, the partition direction (horizontal direction or vertical direction) of the binary tree structure, the partition form of the binary tree structure (symmetric partition or asymmetric partition) ), information indicating whether the unit/block is partitioned in a ternary tree structure, the partition direction of the ternary tree structure (horizontal direction or vertical direction), prediction scheme (intra prediction or inter prediction), intra prediction mode/direction, reference Sample filtering method, predictive block filtering method, predictive block boundary filtering method, filter taps for filtering, filter coefficients for filtering, inter prediction mode, motion information, motion vector, reference picture index, inter prediction direction, inter prediction indicator, reference picture list, reference picture, motion vector predictor, motion vector prediction candidate, motion vector candidate list, information indicating whether merge mode is used, merge candidate, merge candidate list, indicating skip mode Information about whether it is used, the type of interpolation filter, the taps of the interpolation filter, the filter coefficients of the interpolation filter, the size of the motion vector, the accuracy of the motion vector representation, the transform type, the transform size, indicating whether the first transform is used or not information, information indicating whether the additional (secondary) transform is used, first transform index, second transform index, information indicating the presence or absence of residual signal, coding block style, coding block flag, quantization parameter, quantization matrix, Information about the in-loop filter, information indicating whether the in-loop filter is applied, coefficients of the in-loop filter, taps of the in-loop filter, shape/form of the in-loop filter, indicating deblocking information whether the filter is applied, coefficients of the deblocking filter, taps of the deblocking filter, deblocking filter strength, shape/form of the deblocking filter, information indicating whether adaptive sample offset is applied, value of adaptive sample offset, type of adaptive sample offset, type of adaptive sample offset, information indicating whether adaptive loop filter is applied, coefficients of adaptive loop filter, self Taps of adaptive loop filter, shape/form of adaptive loop filter, binarization/de-binarization method, context model, context model decision method, context model update method, information indicating whether the normal mode is executed or not , information indicating whether bypass mode is executed, context bin, bypass bin, transform coefficient, transform coefficient level, transform coefficient level scanning method, image display/output order, slice identification information, slice type , slice partition information, parallel block identification information, parallel block type, parallel block partition information, picture type, bit depth, information on luminance signals, and information on chrominance signals. The prediction scheme may represent one of an intra prediction mode and an inter prediction mode.

The residual signal may represent the difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming the difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming and quantizing the difference between the original signal and the predicted signal. The residual block may be a residual signal for the block.

Here, signaling the flag or index may mean that the encoding apparatus 100 includes an entropy-coded flag or an entropy-coded index generated by performing entropy encoding on the flag or index in the bitstream, and may mean that the decoding apparatus 200 performs entropy coding by the decoding apparatus 200 The entropy-coded flag or entropy-coded index extracted from the stream performs entropy decoding to obtain the flag or index.

Since the encoding apparatus 100 performs encoding via inter prediction, the encoded target image can be used as a reference image for another image to be subsequently processed. Accordingly, the encoding apparatus 100 may reconstruct or decode the encoded target image, and store the reconstructed or decoded image in the reference picture buffer 190 as a reference image. For decoding, inverse quantization and inverse transformation of the encoded target image may be performed.

The quantized levels may be inverse quantized by the inverse quantization unit 160 and inversely transformed by the inverse transform unit 170 . The coefficients that have been inverse quantized and/or inverse transformed may be added to the prediction block by an adder 175 . The inverse-quantized and/or inverse-transformed coefficients and the prediction block are added, and then the reconstructed block can be generated. Here, the inversely quantized and/or inversely transformed coefficients may represent coefficients on which one or more of inverse quantization and inverse transformations are performed, and may also represent a reconstructed residual block.

The reconstructed block may be filtered by filter unit 180 . Filter unit 180 may apply one or more of a deblocking filter, a sample adaptive offset (SAO) filter, and an adaptive loop filter (ALF) to the reconstructed block or reconstructed picture. Filter unit 180 may also be referred to as a "loop filter".

A deblocking filter removes block distortions that occur at boundaries between blocks. In order to determine whether to apply the deblocking filter, a decision may be made on the number of columns or rows of pixels that are included in the block and include the determination of whether to apply the deblocking filter to the target block.

When a deblocking filter is applied to a target block, the applied filter may vary according to the required strength of deblocking filtering. In other words, among different filters, a filter decided in consideration of the strength of deblocking filtering may be applied to the target block. When the deblocking filter is applied to the target block, a filter corresponding to any one of the strong filter and the weak filter may be applied to the target block according to the required strength of the deblocking filter.

Also, when vertical filtering and horizontal filtering are performed on the target block, horizontal filtering and vertical filtering may be performed in parallel.

SAO can add the appropriate offset to the pixel value to compensate for encoding errors. SAO may perform a correction on the image to which deblocking is applied on a pixel-by-pixel basis, where the correction uses the offset of the difference between the original image and the image to which deblocking is applied. In order to perform offset correction for an image, a method for dividing pixels included in the image into a certain number of areas, determining an area to which offset is to be applied among the divided areas, and applying the offset to the determined area may be used. area method, and a method for applying offsets that takes into account edge information for each pixel may also be used.

The ALF may perform filtering based on values obtained by comparing the reconstructed image with the original image. After the pixels included in the image have been divided into a predetermined number of groups, a filter to be applied to each group may be determined, and filtering may be performed differently for each group. For luma signals, information on whether to apply an adaptive loop filter may be signaled for each CU. The shape and filter coefficients of the ALF to be applied to each block may be different for each block. Alternatively, ALF with a fixed form can be applied to the block regardless of the characteristics of the block.

The reconstructed blocks or reconstructed images filtered by the filter unit 180 may be stored in the reference picture buffer 190 . The reconstructed block filtered by the filter unit 180 may be part of the reference picture. In other words, the reference picture may be a reconstructed picture composed of reconstructed blocks filtered by the filter unit 180 . The stored reference pictures can then be used for inter prediction.

FIG. 2 is a block diagram showing the configuration of an embodiment of a decoding apparatus to which the present disclosure is applied.

The decoding device 200 may be a decoder, a video decoding device, or an image decoding device.

2, the decoding apparatus 200 may include an entropy decoding unit 210, an inverse quantization (inverse quantization) unit 220, an inverse transform unit 230, an intra prediction unit 240, an inter prediction unit 250, a switch 245, an adder 255, a filter unit 260 and reference picture buffer 270.

The decoding apparatus 200 may receive the bit stream output from the encoding apparatus 100 . The decoding apparatus 200 may receive a bitstream stored in a computer-readable storage medium, and may receive a bitstream streamed through a wired/wireless transmission medium.

The decoding apparatus 200 may perform decoding on the bitstream in the intra mode and/or the inter mode. Also, the decoding apparatus 200 may generate a reconstructed image or a decoded image through decoding, and may output the reconstructed image or the decoded image.

For example, the operation of switching to the intra mode or the inter mode based on the prediction mode used for decoding may be performed by the switch 245 . When the prediction mode for decoding is the intra mode, the switch 245 may be operated to switch to the intra mode. When the prediction mode for decoding is the inter mode, the switch 245 may be operated to switch to the inter mode.

The decoding apparatus 200 may obtain a reconstructed residual block by decoding an input bitstream, and may generate a prediction block. When the reconstructed residual block and the prediction block are acquired, the decoding apparatus 200 may generate a reconstructed block that is a target of decoding by adding the reconstructed residual block and the prediction block.

The entropy decoding unit 210 may generate symbols by performing entropy decoding on the bitstream based on a probability distribution of the bitstream. The generated symbols may include quantized transform coefficient level format symbols. Here, the entropy decoding method may be similar to the entropy encoding method described above. That is, the entropy decoding method may be an inverse process of the entropy encoding method described above.

The entropy decoding unit 210 may change coefficients in the form of a one-dimensional (1D) vector into a 2D block shape through a transform coefficient scanning method in order to decode the quantized transform coefficient levels.

For example, the coefficients of the block can be changed to a 2D block shape by scanning the block coefficients using an upper right diagonal scan. Alternatively, which of the upper right diagonal scan, vertical scan and horizontal scan will be used may be determined according to the size of the corresponding block and/or the intra prediction mode.

The quantized coefficients may be inverse quantized by the inverse quantization unit 220 . The inverse quantization unit 220 may generate inverse quantized coefficients by performing inverse quantization on the quantized coefficients. In addition, the inversely quantized coefficients may be inversely transformed by the inverse transform unit 230 . The inverse transform unit 230 may generate a reconstructed residual block by performing an inverse transform on the inversely quantized coefficients. As a result of performing inverse quantization and inverse transform on the quantized coefficients, a reconstructed residual block may be generated. Here, when generating the reconstructed residual block, the inverse quantization unit 220 may apply a quantization matrix to the quantized coefficients.

When using the intra mode, the intra prediction unit 240 may generate a prediction block by performing spatial prediction using pixel values of previously decoded neighboring blocks around the target block.

Inter prediction unit 250 may include a motion compensation unit. Alternatively, the inter prediction unit 250 may be designated as a "motion compensation unit".

When the inter mode is used, the motion compensation unit 250 may generate a prediction block by performing motion compensation using motion vectors and reference images stored in the reference picture buffer 270 .

The motion compensation unit may apply an interpolation filter to a partial region of the reference image when the motion vector has a value other than an integer, and may generate a prediction block using the reference image to which the interpolation filter is applied. To perform motion compensation, the motion compensation unit may determine, on a CU basis, which of skip mode, merge mode, advanced motion vector prediction (AMVP) mode, and current picture reference mode corresponds to motion compensation for PUs included in the CU method, and motion compensation may be performed according to the determined mode.

The reconstructed residual block and the prediction block may be added to each other by the adder 255 . The adder 255 may generate a reconstructed block by adding the reconstructed residual block and the prediction block.

The reconstructed block may be filtered by filter unit 260 . The filter unit 260 may apply at least one of a deblocking filter, a SAO filter, and an ALF to the reconstructed block or the reconstructed image. The reconstructed image may be a picture including reconstructed blocks.

The filtered reconstructed image may be output by the encoding device 100 and used by the encoding device.

The reconstructed image filtered by the filter unit 260 may be stored in the reference picture buffer 270 as a reference picture. The reconstructed block filtered by the filter unit 260 may be part of the reference picture. In other words, the reference picture may be an image composed of reconstructed blocks filtered by the filter unit 260 . The stored reference pictures can then be used for inter prediction.

FIG. 3 is a diagram schematically showing a partition structure of an image when the image is encoded and decoded.

FIG. 3 may schematically illustrate an example in which a single unit is partitioned into a plurality of subunits.

To efficiently partition an image, coding units (CUs) may be used in encoding and decoding. The term "unit" may be used to collectively designate 1) a block comprising image samples and 2) a syntax element. For example, "partition of a unit" may mean "partition of a block corresponding to a unit".

A CU may be used as a basic unit for image encoding/decoding. The CU may be used as a unit to which one mode selected from the intra mode and the inter mode is applied in image encoding/decoding. In other words, in image encoding/decoding, it may be determined which of the intra mode and the inter mode is to be applied to each CU.

Also, a CU may be a basic unit for predicting, transforming, quantizing, inverse transforming, inverse quantizing, and encoding/decoding transform coefficients.

3, a picture 300 may be sequentially partitioned into units corresponding to a largest coding unit (LCU), and a partition structure may be determined for each LCU. Here, LCU may be used to have the same meaning as Coding Tree Unit (CTU).

Partitioning a cell may mean partitioning a block corresponding to the cell. The block partition information may include depth information about the depth of the unit. The depth information may indicate the number of times the cell is partitioned and/or the extent to which the cell is partitioned. A single unit can be hierarchically partitioned into subunits, while the single unit has depth information based on a tree structure. Each partitioned subunit may have depth information. The depth information may be information indicating the size of the CU. Depth information may be stored for each CU.

Each CU may have depth information. When a CU is partitioned, the depth of the CU generated from the partition may be increased by 1 from the depth of the partitioned CU.

The partition structure may represent the distribution of coding units (CUs) in the LCU 310 that are used to efficiently encode pictures. This distribution may be determined depending on whether a single CU is to be partitioned into multiple CUs. The number of CUs generated by partitioning may be a positive integer of 2 or more, including 2, 3, 4, 8, 16, and so on. According to the number of CUs generated by partitioning, the horizontal size and vertical size of each CU generated by partitioning may be smaller than those of the CU before being partitioned.

Each partitioned CU may be recursively partitioned into four CUs in the same manner. Via recursive partitioning, at least one of the horizontal size and the vertical size of each partitioned CU may be reduced compared to at least one of the horizontal size and the vertical size of the CU before being partitioned.

Partitioning of a CU may be performed recursively up to a predefined depth or a predefined size. For example, the depth of a CU may have a value ranging from 0 to 3. Depending on the depth of the CU, the size of the CU may range from size 64x64 to size 8x8.

For example, the depth of the LCU may be 0, and the depth of the smallest coding unit (SCU) may be a predefined maximum depth. Here, as described above, the LCU may be the CU having the largest coding unit size, and the SCU may be the CU having the smallest coding unit size.

Partitioning may begin at LCU 310, and the depth of the CU may increase by one whenever the horizontal size and/or vertical size of the CU is reduced by partitioning.

For example, an unpartitioned CU may have a size of 2Nx2N for each depth. Also, in the case where a CU is partitioned, a CU of size 2N×2N may be partitioned into four CUs each of size N×N. The value of N can be halved each time the depth increases by 1.

Referring to FIG. 3 , an LCU with a depth of 0 may have 64×64 pixels or a block of 64×64. 0 can be the minimum depth. A depth-3 SCU may have 8x8 pixels or 8x8 blocks. 3 can be the maximum depth. Here, a CU having a block of 64×64, which is an LCU, may be represented by depth 0. A CU with a block of 32x32 may be represented with a depth of 1. A CU with 16x16 blocks may be represented with a depth of 2. A CU having a block of 8×8 that is an SCU may be represented by a depth of 3.

The information on whether the corresponding CU is partitioned may be represented by the partition information of the CU. The partition information may be 1-bit information. All CUs except SCUs may include partition information. For example, the value of partition information of a CU that is not partitioned may be 0. The value of the partition information of the partitioned CU may be 1.

For example, when a single CU is partitioned into four CUs, the horizontal and vertical sizes of each of the four CUs generated by partitioning may be half of those of the CU before being partitioned. When a CU having a size of 32×32 is partitioned into four CUs, the size of each of the four partitioned CUs may be 16×16. When a single CU is partitioned into four CUs, the CUs may be considered to have been partitioned in a quad-tree structure.

For example, when a single CU is partitioned into two CUs, the horizontal or vertical size of each of the two CUs generated by partitioning may be half the horizontal or vertical size of the CU before being partitioned. When a CU having a size of 32×32 is vertically partitioned into two CUs, the size of each of the two partitioned CUs may be 16×32. When a CU having a size of 32×32 is horizontally partitioned into two CUs, the size of each of the partitioned two CUs may be 32×16. When a single CU is partitioned into two CUs, the CUs may be considered to have been partitioned in a binary tree structure.

Both quad-tree partitioning and binary-tree partitioning are applied to the LCU 310 of FIG. 3 .

In the encoding apparatus 100, a coding tree unit (CTU) having a size of 64×64 may be partitioned into a plurality of smaller CUs through a recursive quad-tree structure. A single CU may be partitioned into four CUs with the same size. Each CU may be recursively partitioned and may have a quadtree structure.

Through recursive partitioning of the CU, the optimal partitioning method that incurs the least rate-distortion cost can be selected.

FIG. 4 is a diagram illustrating a form of a prediction unit (PU) that a coding unit (CU) can include.

Among the CUs partitioned from the LCU, the CUs that are no longer partitioned may be divided into one or more prediction units (PUs). This division is also called "partitioning".

A PU may be a basic unit for prediction. The PU may be encoded and decoded in any one of skip mode, inter mode, and intra mode. The PU can be partitioned into various shapes according to each mode. For example, the target block described above with reference to FIG. 1 and the target block described above with reference to FIG. 2 may both be PUs.

A CU may not be divided into PUs. When the CU is not divided into PUs, the size of the CU and the size of the PU may be equal to each other.

In skip mode, there may be no partitions in the CU. In skip mode, the 2Nx2N mode 410, in which the size of the PU and the size of the CU are the same as each other, may be supported without partitioning.

In inter mode, there can be 8 types of partition shapes in a CU. For example, in inter mode, 2N×2N mode 410, 2N×N mode 415, N×2N mode 420, N×N mode 425, 2N×nU mode 430, 2N×nD mode 435, nL×2N mode can be supported 440 and nR×2N mode 445.

In intra mode, 2Nx2N mode 410 and NxN mode 425 may be supported.

In 2Nx2N mode 410, a PU of size 2Nx2N may be encoded. A PU of size 2N×2N may represent a PU of the same size as that of a CU. For example, a PU of size 2Nx2N may have size 64x64, 32x32, 16x16, or 8x8.

In NxN mode 425, a PU of size NxN may be encoded.

For example, in intra prediction, when the size of the PU is 8×8, four partitioned PUs may be encoded. The size of each partitioned PU may be 4×4.

When the PU is encoded in intra mode, the PU may be encoded using any one of multiple intra prediction modes. For example, HEVC techniques may provide 35 intra-prediction modes under which a PU may be encoded.

Which of the 2Nx2N mode 410 and the NxN mode 425 will be used to encode the PU may be determined based on a rate-distortion cost.

The encoding apparatus 100 may perform an encoding operation on a PU having a size of 2N×2N. Here, the encoding operation may be an operation of encoding the PU in each of a plurality of intra prediction modes that can be used by the encoding apparatus 100 . Through encoding operations, the optimal intra prediction mode for a PU of size 2Nx2N can be derived. The optimal intra prediction mode may be an intra prediction mode in which the smallest rate-distortion cost occurs when encoding a PU of size 2N×2N among a plurality of intra prediction modes that can be used by the encoding apparatus 100 .

Also, the encoding apparatus 100 may sequentially perform encoding operations on respective PUs obtained by performing N×N partitioning. Here, the encoding operation may be an operation of encoding the PU in each of a plurality of intra prediction modes that can be used by the encoding apparatus 100 . Through encoding operations, the optimal intra prediction mode for a PU of size NxN can be derived. The optimal intra prediction mode may be an intra prediction mode in which the smallest rate-distortion cost occurs when encoding a PU of size N×N among a plurality of intra prediction modes that can be used by the encoding apparatus 100 .

The encoding apparatus 100 may determine, based on a comparison between a rate-distortion cost of a PU of size 2N×2N and a rate-distortion cost of a PU of size N×N, among a PU of size 2N×2N and a PU of size N×N which will be encoded.

A single CU may be partitioned into one or more PUs, and a PU may be partitioned into multiple PUs.

For example, when a single PU is partitioned into four PUs, the horizontal and vertical sizes of each of the four PUs generated by partitioning may be half of those of the PU before being partitioned. When a PU of size 32x32 is partitioned into four PUs, the size of each of the four partitioned PUs may be 16x16. When a single PU is partitioned into four PUs, the PUs can be considered to have been partitioned in a quad-tree structure.

For example, when a single PU is partitioned into two PUs, the horizontal or vertical size of each of the two PUs generated by partitioning may be half the horizontal or vertical size of the PU before being partitioned. When a PU of size 32x32 is vertically partitioned into two PUs, the size of each of the two partitioned PUs may be 16x32. When a PU of size 32x32 is horizontally partitioned into two PUs, the size of each of the two partitioned PUs may be 32x16. When a single PU is partitioned into two PUs, the PUs can be considered to have been partitioned in a binary tree structure.

FIG. 5 is a diagram illustrating a form of a transform unit (TU) that can be included in a CU.

A transform unit (TU) may be a basic unit in a CU that is used for processes such as transform, quantization, inverse transform, inverse quantization, entropy encoding, and entropy decoding.

A TU may have a square shape or a rectangular shape. The shape of the TU may be determined based on the size and/or shape of the CU.

In a CU partitioned from an LCU, a CU that is no longer partitioned as a CU may be partitioned into one or more TUs. Here, the partition structure of the TU may be a quadtree structure. For example, as shown in FIG. 5, a single CU 510 may be partitioned one or more times according to a quadtree structure. Through such partitioning, a single CU 510 may be composed of TUs of various sizes.

It can be considered that a CU is recursively divided when a single CU is divided two or more times. Through partitioning, a single CU may be composed of transform units (TUs) with various sizes.

Optionally, a single CU may be divided into one or more TUs based on the number of vertical and/or horizontal lines dividing the CU.

CUs can be divided into symmetric TUs or asymmetric TUs. In order to divide into asymmetric TUs, information about the size and/or shape of each TU may be signaled from the encoding apparatus 100 to the decoding apparatus 200 . Optionally, the size and/or shape of each TU may be derived from information about the size and/or shape of the CU.

A CU may not be divided into TUs. When the CU is not divided into TUs, the size of the CU and the size of the TU may be equal to each other.

A single CU may be partitioned into one or more TUs, and a TU may be partitioned into multiple TUs.

For example, when a single TU is partitioned into four TUs, the horizontal and vertical sizes of each of the four TUs generated by partitioning may be half of those of the TU before being partitioned. When a TU of size 32x32 is partitioned into four TUs, the size of each of the four partitioned TUs may be 16x16. When a single TU is partitioned into four TUs, the TUs can be considered to have been partitioned in a quad-tree structure.

For example, when a single TU is partitioned into two TUs, the horizontal or vertical size of each of the two TUs generated by partitioning may be half the horizontal or vertical size of the TU before being partitioned. When a TU of size 32x32 is vertically partitioned into two TUs, the size of each of the two partitioned TUs may be 16x32. When a TU of size 32x32 is horizontally partitioned into two TUs, the size of each of the two partitioned TUs may be 32x16. When a single TU is partitioned into two TUs, the TUs can be considered to have been partitioned in a binary tree structure.

FIG. 6 shows the division of blocks according to an example.

In the video encoding and/or decoding process, as shown in FIG. 6, target blocks may be divided.

For the division of the target block, an indicator indicating division information may be signaled from the encoding apparatus 100 to the decoding apparatus 200 . The division information may be information indicating how the target block is divided.

The division information may be a division flag (hereinafter referred to as "split_flag"), a quad-binary flag (hereinafter referred to as "QB_flag"), a quadtree flag (hereinafter referred to as "quadtree_flag"), a binary tree flag (hereinafter referred to as "binarytree_flag") ) and one or more of a binary type flag (hereinafter referred to as "Btype_flag").

'split_flag' may be a flag indicating whether the block is divided. For example, a split_flag value of 1 may indicate that the corresponding block is split. A split_flag value of 0 may indicate that the corresponding block is not split.

"QB_flag" may be a flag indicating which of the quad-tree form and the binary-tree form corresponds to the shape in which the block is divided. For example, a QB_flag value of 0 may indicate that the block is partitioned in a quadtree. A QB_flag value of 1 may indicate that the block is partitioned in a binary tree. Optionally, a QB_flag value of 0 may indicate that the block is divided in a binary tree. A QB_flag value of 1 may indicate that the block is partitioned in a quadtree.

'quadtree_flag' may be a flag indicating whether a block is divided in a quadtree form. For example, a quadtree_flag value of 1 may indicate that the block is divided in a quadtree. A quadtree_flag value of 0 may indicate that the block is not partitioned in a quadtree.

"binarytree_flag" may be a flag indicating whether the block is divided in a binary tree form. For example, a binarytree_flag value of 1 may indicate that the block is divided in a binary tree. A binarytree_flag value of 0 may indicate that the block is not divided in a binary tree.

'Btype_flag' may be a flag indicating which of vertical division and horizontal division corresponds to the division direction when the block is divided in a binary tree form. For example, a Btype_flag value of 0 may indicate that the block is divided in the horizontal direction. A Btype_flag value of 1 may indicate that the block is divided in the vertical direction. Alternatively, a Btype_flag value of 0 may indicate that the block is divided in the vertical direction. A Btype_flag value of 1 may indicate that the block is divided in the horizontal direction.

For example, partition information for the block in FIG. 6 may be derived by signaling at least one of quadtree_flag, binarytree_flag, and Btype_flag, as shown in Table 1 below.

Table 1

For example, the split information for the block in FIG. 6 may be derived by signaling at least one of split_flag, QB_flag, and Btype_flag, as shown in Table 2 below.

Table 2

The partitioning method may be limited to quadtree or binary tree depending on the size and/or shape of the block. When this restriction is applied, split_flag may be a flag indicating whether the block is divided in the form of a quad-tree or a flag indicating whether the block is divided in the form of a binary tree. The size and shape of the block may be derived from the depth information of the block, and the depth information may be signaled from the encoding apparatus 100 to the decoding apparatus 200 .

Partitioning in the form of a quadtree is only possible when the size of the block falls within a certain range. For example, the specific range may be defined by at least one of a maximum block size and a minimum block size that can be divided only in the form of a quadtree.

Information indicating the maximum block size and the minimum block size that can be divided only in the form of a quadtree may be signaled from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream. Furthermore, this information may be signaled for at least one of units such as videos, sequences, pictures, and slices (or segments).

Alternatively, the maximum block size and/or the minimum block size may be fixed sizes predefined by the encoding apparatus 100 and the decoding apparatus 200 . For example, when the size of the block is larger than 64x64 and smaller than 256x256, only division in the form of a quadtree is possible. In this case, split_flag may be a flag indicating whether to perform division in a quadtree form.

Partitioning in binary tree form is only possible when the size of the block falls within a certain range. For example, the specific range may be defined by at least one of a maximum block size and a minimum block size that can be divided only in a binary tree.

Information indicating the maximum block size and/or the minimum block size that can be divided only in a binary tree form may be signaled from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream. Furthermore, this information may be signaled for at least one of units such as sequences, pictures, and slices (or slices).

Alternatively, the maximum block size and/or the minimum block size may be fixed sizes predefined by the encoding apparatus 100 and the decoding apparatus 200 . For example, when the size of the block is larger than 8×8 and smaller than 16×16, only division in the form of a binary tree is possible. In this case, split_flag may be a flag indicating whether to perform division in the form of a binary tree.

The division of blocks may be restricted by previous divisions. For example, when a block is divided in the form of a binary tree and a plurality of partitioned blocks are generated, each of the partitioned blocks may be additionally divided only in the form of a binary tree.

When the horizontal size or vertical size of the partition block is a size that cannot be further divided, the above-mentioned indicator may not be signaled.

FIG. 7 is a diagram for explaining an embodiment of intra prediction processing.

Arrows extending radially from the center of the graph in FIG. 7 indicate the prediction directions of the intra prediction modes. Also, numbers appearing near the arrows may represent examples of mode values assigned to the intra prediction mode or assigned to the prediction direction of the intra prediction mode.

Intra-coding and/or decoding may be performed using reference samples of blocks adjacent to the target block. Neighboring blocks may be neighboring reconstructed blocks. For example, intra-frame encoding and/or decoding may be performed using values of reference samples included in each adjacent reconstructed block or encoding parameters of adjacent reconstructed blocks.

The encoding apparatus 100 and/or the decoding apparatus 200 may generate the prediction block by performing intra prediction on the target block based on the information on the samples in the target image. When intra prediction is performed, the encoding apparatus 100 and/or the decoding apparatus 200 may generate a prediction block for the target block by performing intra prediction based on information about samples in the target image. When intra prediction is performed, the encoding apparatus 100 and/or the decoding apparatus 200 may perform directional prediction and/or non-directional prediction based on at least one reconstructed reference sample.

The prediction block may be a block generated as a result of performing intra prediction. A prediction block may correspond to at least one of a CU, PU, and TU.

A unit of a prediction block may have a size corresponding to at least one of a CU, PU, and TU. The prediction block may have a square shape of size 2Nx2N or NxN. Dimensions NxN may include dimensions 4x4, 8x8, 16x16, 32x32, 64x64, and the like.

Alternatively, the prediction block may be a square block of size 2x2, 4x4, 8x8, 16x16, 32x32, 64x64, etc. or a size of 2x8, 4x8, 2x Rectangular blocks of 16, 4x16, 8x16, etc.

Intra prediction may be performed considering the intra prediction mode for the target block. The number of intra prediction modes that the target block may have may be a predefined fixed value, and may be a value determined differently according to properties of the prediction block. For example, the properties of the prediction block may include the size of the prediction block, the type of the prediction block, and the like.

For example, the number of intra prediction modes may be fixed to 35 regardless of the size of the prediction block. Alternatively, the number of intra prediction modes may be, for example, 3, 5, 9, 17, 34, 35 or 36.

The intra prediction mode may be a non-directional mode or a directional mode. For example, as shown in FIG. 7, the intra prediction modes may include two non-directional modes and 33 directional modes.

The two non-directional modes may include DC mode and planar mode.

The directional pattern may be a pattern with a specific direction or a specific angle.

Each of the intra prediction modes may be represented by at least one of a mode number, a mode value, and a mode angle. The number of intra prediction modes may be M. The value of M can be 1 or greater. In other words, the number of intra prediction modes may be M, where M includes the number of non-directional modes and the number of directional modes.

The number of intra prediction modes may be fixed to M regardless of the size of the block. For example, the number of intra prediction modes may be fixed to any one of 35 and 67 regardless of the size of the block.

Alternatively, the number of intra prediction modes may vary according to the size of the block and/or the type of color components.

For example, the larger the size of the block, the larger the number of intra prediction modes. Optionally, the larger the size of the block, the smaller the number of intra prediction modes. When the size of the block is 4×4 or 8×8, the number of intra prediction modes may be 67. When the size of the block is 16×16, the number of intra prediction modes may be 35. When the size of the block is 32×32, the number of intra prediction modes may be 19. When the size of the block is 64×64, the number of intra prediction modes may be seven.

For example, the number of intra prediction modes may differ depending on whether the color component is a luminance signal or a chrominance signal. Alternatively, the number of intra prediction modes corresponding to luma component blocks may be greater than the number of intra prediction modes corresponding to chroma component blocks.

For example, in a vertical mode with a mode value of 26, prediction may be performed in the vertical direction based on pixel values of reference samples. For example, in a horizontal mode with a mode value of 10, prediction may be performed in the horizontal direction based on pixel values of reference samples.

Even in a direction mode other than the above-described modes, the encoding apparatus 100 and the decoding apparatus 200 may perform intra prediction on the target unit using reference samples according to angles corresponding to the direction mode.

The intra prediction mode located on the right side with respect to the vertical mode may be referred to as "vertical-right mode". The intra prediction mode located below the horizontal mode may be referred to as a "horizontal-down mode". For example, in FIG. 7 , the intra prediction mode whose mode value is one of 27, 28, 29, 30, 31, 32, 33, and 34 may be the vertical-right mode 613. The intra prediction mode whose mode value is one of 2, 3, 4, 5, 6, 7, 8, and 9 may be the horizontal-down mode 616 .

Non-directional modes may include DC mode and planar mode. For example, the value of DC mode may be 1. The value of flat mode can be 0.

Orientation patterns may include angle patterns. Among the plurality of intra prediction modes, the remaining modes other than the DC mode and the planar mode may be directional modes.

When the intra prediction mode is the DC mode, the prediction block may be generated based on an average value of pixel values of a plurality of reference pixels. For example, the value of the pixel of the prediction block may be determined based on an average value of pixel values of a plurality of reference pixels.

The number of intra prediction modes and the mode value of each intra prediction mode described above are only exemplary. The number of intra-prediction modes described above and the mode value of each intra-prediction mode may be defined differently depending on the embodiment, implementation, and/or requirements.

In order to perform intra prediction on the target block, a step of checking whether samples included in the reconstructed adjacent blocks can be used as reference samples for the target block may be performed. When a sample that cannot be used as a reference sample of the target block exists among the samples in the neighboring block, via interpolation using at least one sample value among the samples included in the reconstructed neighboring block and/or Or copy the resulting value to replace the sample value of a sample that cannot be used as a reference sample. When a sample value of an existing sample is replaced by a value generated via copying and/or interpolation, that sample may be used as a reference sample for the target block.

In intra prediction, a filter may be applied to at least one of reference samples and prediction samples based on at least one of an intra prediction mode and a size of a target block.

The type of filter to be applied to at least one of the reference samples and the prediction samples may be different according to at least one of the intra prediction mode of the target block, the size of the target block, and the shape of the target block. The types of filters may be classified according to one or more of the number of filter taps, the values of filter coefficients, and filter strength.

When the intra prediction mode is the plane mode, the upper reference sample of the target block, the left reference sample of the target block, the A weighted sum of the upper right reference samples and the lower left reference samples of the target block is used to generate the sample value of the prediction target block.

When the intra prediction mode is the DC mode, the average value of the reference samples above the target block and the reference samples to the left of the target block may be used when generating the prediction block of the target block. Also, filtering using the values of the reference samples may be performed on a specific row or a specific column in the target block. A particular row may be one or more upper rows adjacent to the reference sample. A particular column may be one or more left columns adjacent to the reference sample.

When the intra prediction mode is the directional mode, the prediction block may be generated using upper reference samples, left reference samples, upper right reference samples and/or lower left reference samples of the target block.

In order to generate the predicted samples described above, real-number based interpolation may be performed.

The intra prediction mode of the target block may be predicted from the intra prediction modes of neighboring blocks adjacent to the target block, and information for prediction may be entropy encoded/entropy decoded.

For example, when the intra prediction modes of the target block and the adjacent blocks are the same as each other, a predefined flag may be used to signal that the intra prediction modes of the target block and the adjacent blocks are the same.

For example, an indicator for indicating the same intra prediction mode as the intra prediction mode of the target block among the intra prediction modes of a plurality of adjacent blocks may be signaled.

When the intra prediction modes of the target block and the neighboring blocks are different from each other, the information on the intra prediction mode of the target block may be encoded and/or decoded using entropy encoding and/or entropy decoding.

FIG. 8 is a diagram for explaining the positions of reference samples used in the intra prediction process.

FIG. 8 shows the positions of reference samples used for intra prediction of the target block. Referring to FIG. 8 , the reconstructed reference samples used for intra prediction of the target block may include a lower left reference sample 831, a left reference sample 833, an upper left reference sample 835, an upper reference sample 837, and an upper right reference sample 839 .

For example, the left reference sample 833 may represent the reconstructed reference pixel adjacent to the left side of the target block. Upper reference samples 837 may represent reconstructed reference pixels adjacent to the top of the target block. The upper left reference sample 835 may represent the reconstructed reference pixel located at the upper left corner of the target block. The lower left reference sample 831 may represent a reference sample located below the left sample line among samples located on the same line as the left sample line composed of the left reference sample 833 . The upper right reference sample 839 may represent a reference sample located to the right of the upper sample line among samples located on the same line as the upper sample line composed of the upper reference sample 837 .

When the size of the target block is N×N, the numbers of the lower left reference samples 831 , the left reference samples 833 , the upper reference samples 837 , and the upper right reference samples 839 may all be N.

The predicted block may be generated by performing intra prediction on the target block. The process of generating the prediction block may include determining values for pixels in the prediction block. The size of the target block and the prediction block may be the same.

The reference samples used for intra prediction of the target block may vary according to the intra prediction mode of the target block. The direction of the intra prediction mode may represent the dependency between the reference samples and the pixels of the prediction block. For example, a value specifying a reference sample may be used as a value specifying one or more pixels in the prediction block. In this case, the designated reference samples and the one or more designated pixels in the prediction block may be samples and pixels located on a straight line in the direction of the intra prediction mode. In other words, the value of the specified reference sample can be copied as the value of the pixel located in the direction opposite to that of the intra prediction mode. Alternatively, the value of a pixel in the prediction block may be the value of a reference sample located in the direction of the intra prediction mode with respect to the position of the pixel.

In an example, when the intra prediction mode of the target block is a vertical mode with a mode value of 26, the upper reference sample 837 may be used for intra prediction. When the intra prediction mode is the vertical mode, the value of a pixel in the prediction block may be the value of a reference sample located vertically above the position of the pixel. Therefore, the upper reference sample 837 adjacent to the top of the target block can be used for intra prediction. Furthermore, the values of the pixels in a row of the prediction block may be the same as the values of the pixels of the upper reference sample 837 .

In an example, when the intra prediction mode of the target block is a horizontal mode with a mode value of 10, the left reference sample 833 may be used for intra prediction. When the intra prediction mode is the horizontal mode, the value of a pixel in the prediction block may be the value of a reference sample located horizontally to the left of the position of the pixel. Therefore, the left reference sample 833 adjacent to the left side of the target block can be used for intra prediction. Furthermore, the values of the pixels in one column of the prediction block may be the same as the values of the pixels of the left reference sample 833 .

In an example, when the mode value of the intra prediction mode of the current block is 18, at least some of the left reference samples 833, the upper left reference samples 835, and the upper reference samples 837 may be used for Intra prediction. When the mode value of the intra prediction mode is 18, the value of the pixel in the prediction block may be the value of the reference sample diagonally located at the upper left corner of the pixel.

Also, in the case where an intra prediction mode with a mode value of 27, 28, 29, 30, 31, 32, 33 or 34 is used, at least a part of the upper right reference samples 839 may be used for intra prediction.

Also, in the case where an intra prediction mode with a mode value of 2, 3, 4, 5, 6, 7, 8, or 9 is used, at least a part of the lower left reference samples 831 may be used for intra prediction.

Also, in the case of an intra prediction mode in which the mode value is a value ranging from 11 to 25, the upper left reference sample 835 may be used for intra prediction.

The number of reference samples used to determine the pixel value of one pixel in the prediction block may be 1 or 2 or more.

As described above, the pixel value of the pixel in the prediction block may be determined according to the position of the pixel and the position of the reference sample indicated by the direction of the intra prediction mode. When the position of the pixel and the position of the reference sample indicated by the direction of the intra prediction mode are integer positions, the value of one reference sample indicated by the integer position may be used to determine the pixel value of the pixel in the prediction block .

When the position of the pixel and the position of the reference sample indicated by the direction of the intra prediction mode are not integer positions, an interpolated reference sample based on the two closest reference samples to the position of the reference sample may be generated. The values of the interpolated reference samples may be used to determine pixel values for pixels in the prediction block. In other words, when the position of the pixel in the prediction block and the position of the reference sample indicated by the direction of the intra prediction mode indicate the position between the two reference samples, a value based on the two samples may be generated the interpolated value.

The prediction block generated via prediction may be different from the original target block. In other words, there may be a prediction error, which is the difference between the target block and the prediction block, and there may also be a prediction error between the pixels of the target block and the pixels of the prediction block.

In the following, the terms "difference", "error" and "residual" may be used to have the same meaning and may be used interchangeably with each other.

For example, in the case of directional intra prediction, the longer the distance between the pixels of the prediction block and the reference samples, the larger the prediction error that may occur. Such prediction errors can lead to discontinuities between the generated prediction block and neighboring blocks.

To reduce prediction errors, filtering operations for prediction blocks may be used. The filtering operation may be configured to adaptively apply filters to regions in the prediction block that are considered to have larger prediction errors. For example, a region considered to have a larger prediction error may be the boundary of a prediction block. Also, a region considered to have a large prediction error in a prediction block may differ according to intra prediction modes, and characteristics of filters may also differ according to intra prediction modes.

FIG. 9 is a diagram for explaining an embodiment of an inter prediction process.

The rectangles shown in FIG. 9 may represent images (or pictures). Furthermore, in FIG. 9, arrows may indicate prediction directions. That is, each picture may be encoded and/or decoded according to the prediction direction.

Pictures may be classified into intra pictures (I pictures), unidirectionally predictive pictures or predictively coded pictures (P pictures), and bidirectionally predictive pictures or bidirectionally predictively coded pictures (B pictures) according to encoding types. Each picture may be encoded and/or decoded according to its encoding type.

When a target image to be encoded is an I picture, the target image can be encoded using data contained in the image itself without performing inter prediction with reference to other images. For example, I pictures may be encoded via intra prediction only.

When the target image is a P picture, the target image may be encoded via inter prediction using reference pictures existing in one direction. Here, the one direction may be a forward direction or a backward direction.

When the target image is a B-picture, the image may be encoded via inter-frame prediction using reference pictures existing in both directions, or may be encoded via frames using reference pictures existing in one of the forward and backward directions Inter prediction encodes images. Here, the two directions may be a forward direction and a backward direction.

P pictures and B pictures encoded and/or decoded using reference pictures may be regarded as pictures using inter prediction.

Hereinafter, the inter prediction in the inter mode according to the embodiment will be described in detail.

Inter prediction may be performed using motion information.

In the inter mode, the encoding apparatus 100 may perform inter prediction and/or motion compensation on the target block. The decoding apparatus 200 may perform inter prediction and/or motion compensation corresponding to the inter prediction and/or motion compensation performed by the encoding apparatus 100 on the target block.

The motion information of the target block may be derived separately by the encoding apparatus 100 and the decoding apparatus 200 during inter prediction. The motion information may be derived using motion information of reconstructed neighboring blocks, motion information of the col block, and/or motion information of blocks adjacent to the col block.

For example, the encoding apparatus 100 or the decoding apparatus 200 may perform prediction and/or motion compensation by using motion information of spatial candidates and/or temporal candidates as motion information of the target block. A target block may represent a PU and/or a PU partition.

Spatial candidates may be reconstructed blocks that are spatially adjacent to the target block.

A temporal candidate may be a reconstructed block corresponding to the target block in a previously reconstructed co-located picture (col picture).

In inter prediction, the encoding apparatus 100 and the decoding apparatus 200 may improve encoding efficiency and decoding efficiency by utilizing motion information of spatial candidates and/or temporal candidates. The motion information of the spatial candidates may be referred to as "spatial motion information". The motion information of the temporal candidates may be referred to as "temporal motion information".

Hereinafter, the motion information of the spatial candidate may be motion information of a PU including the spatial candidate. The motion information of the temporal candidate may be motion information of a PU including the temporal candidate. The motion information of the candidate block may be motion information of a PU including the candidate block.

Inter prediction may be performed using reference pictures.

The reference picture may be at least one of a picture preceding the target picture and a picture following the target picture. The reference picture may be a picture used for prediction of the target block.

In inter prediction, a region in a reference picture may be specified using a reference picture index (or refIdx) for indicating a reference picture, a motion vector to be described later, and the like. Here, the area specified in the reference picture may indicate a reference block.

For inter prediction, a reference picture can be selected, and a reference block corresponding to the target block can also be selected from the reference picture. Also, inter prediction may use the selected reference block to generate a prediction block for the target block.

Motion information may be derived during inter prediction by each of the encoding apparatus 100 and the decoding apparatus 200 .

Spatial candidates may be 1) blocks that exist in the target picture 2) have been previously reconstructed via encoding and/or decoding and 3) are adjacent to or at the corners of the target block. Here, the "block at the corner of the target block" may be a block that is vertically adjacent to a neighboring block that is horizontally adjacent to the target block, or a block that is horizontally adjacent to a neighboring block that is vertically adjacent to the target block. Also, "a block located at the corner of the target block" may have the same meaning as "a block adjacent to the corner of the target block". The meaning of "a block located at the corner of the target block" may be included in the meaning of "a block adjacent to the target block".

For example, a spatial candidate can be a reconstructed block located to the left of the target block, a reconstructed block located above the target block, a reconstructed block located in the lower left corner of the target block, a reconstructed block located in the upper right corner of the target block, or a target block located in the upper left corner of the target block.

Each of the encoding apparatus 100 and the decoding apparatus 200 may identify a block existing at a position spatially corresponding to the target block in the col picture. The position of the target block in the target picture and the position of the identified block in the col picture may correspond to each other.

Each of the encoding apparatus 100 and the decoding apparatus 200 may determine a col block that exists at a predefined relevant position for the identified block as a temporal candidate. The predefined relevant locations may be locations that exist inside and/or outside the identified block.

For example, a col block may include a first col block and a second col block. When the coordinates of the identified block are (xP, yP) and the size of the identified block is denoted by (nPSW, nPSH), the first col block may be the block located at coordinates (xP+nPSW, yP+nPSH). The second col block may be the block located at coordinates (xP+(nPSW>>1), yP+(nPSH>>1)). The second col block is optionally used when the first col block is not available.

The motion vector of the target block may be determined based on the motion vector of the col block. Each of the encoding apparatus 100 and the decoding apparatus 200 may scale the motion vector of the col block. The scaled motion vector of the col block may be used as the motion vector of the target block. Also, the motion vector of the running information of the temporal candidates stored in the list may be a scaled motion vector.

The ratio of the motion vector of the target block to the motion vector of the col block may be the same as the ratio of the first distance to the second distance. The first distance may be a distance between the reference picture and the target picture of the target block. The second distance may be a distance between the reference picture and the col picture of the col block.

The scheme for deriving motion information may vary according to the inter prediction mode of the target block. For example, as the inter prediction mode applied to the inter prediction, there may be an Advanced Motion Vector Predictor (AMVP) mode, a merge mode, a skip mode, a current picture reference mode, and the like. Merge mode may also be referred to as "motion merge mode". Each mode will be described in detail below.

1) AMVP mode

When the AMVP mode is used, the encoding apparatus 100 may search for similar blocks in a neighboring area of the target block. The encoding apparatus 100 may acquire a prediction block by performing prediction on a target block using motion information of the found similar blocks. The encoding apparatus 100 may encode the residual block, which is the difference between the target block and the prediction block.

1-1) Create a list of predicted motion vector candidates

When the AMVP mode is used as the prediction mode, each of the encoding apparatus 100 and the decoding apparatus 200 may create a list of predicted motion vector candidates using motion vectors of spatial candidates, motion vectors of temporal candidates, and zero vectors. The motion vector predictor candidate list may include one or more motion vector predictor candidates. At least one of a motion vector of a spatial candidate, a motion vector of a temporal candidate, and a null vector may be determined and used as a predicted motion vector candidate.

Hereinafter, the terms "prediction motion vector (candidate)" and "motion vector (candidate)" may be used to have the same meaning, and may be used interchangeably with each other.

Hereinafter, the terms "motion vector predictor candidate" and "AMVP candidate" may be used to have the same meaning, and may be used interchangeably with each other.

Hereinafter, the terms "motion vector predictor candidate list" and "AMVP candidate list" may be used to have the same meaning, and may be used interchangeably with each other.

Spatial candidates may include reconstructed spatial neighboring blocks. In other words, the motion vectors of the reconstructed neighboring blocks may be referred to as "spatially predicted motion vector candidates".

Temporal candidates may include the col block and blocks adjacent to the col block. In other words, the motion vector of the col block or the motion vector of the block adjacent to the col block may be referred to as a "temporal motion vector predictor candidate".

The zero vector can be the (0,0) motion vector.

A motion vector predictor candidate may be a motion vector predictor for predicting a motion vector. Also, in the encoding apparatus 100, each predicted motion vector candidate may be an initial search position for a motion vector.

1-2) Searching for motion vectors using the list of predicted motion vector candidates

The encoding apparatus 100 may determine a motion vector to be used for encoding the target block within the search range using the list of predicted motion vector candidates. Also, the encoding apparatus 100 may determine a motion vector predictor candidate to be used as a motion vector predictor of the target block among the motion vector predictor candidates existing in the motion vector predictor candidate list.

The motion vector to be used for encoding the target block may be a motion vector that can be encoded with minimum cost.

Also, the encoding apparatus 100 may determine whether to encode the target block using the AMVP mode.

1-3) Transmission of inter-frame prediction information

The encoding apparatus 100 may generate a bitstream including inter prediction information required for inter prediction. The decoding apparatus 200 may perform inter prediction on the target block using the inter prediction information of the bitstream.

The inter prediction information may include 1) mode information indicating whether AMVP is used, 2) a predicted motion vector index, 3) a motion vector difference (MVD), 4) a reference direction, and 5) a reference picture index.

Hereinafter, the terms "predictor motion vector index" and "AMVP index" may be used to have the same meaning, and may be used interchangeably with each other. Furthermore, the inter prediction information may include residual signals.

When the mode information indicates that the AMVP mode is used, the decoding apparatus 200 may acquire the predicted motion vector index, the MVD, the reference direction, and the reference picture index from the bitstream through entropy decoding.

The motion vector predictor index may indicate a motion vector predictor candidate to be used for prediction of the target block among the motion vector predictor candidates included in the motion vector predictor candidate list.

1-4) Inter prediction in AMVP mode using inter prediction information

The decoding apparatus 200 may derive motion vector predictor candidates using the motion vector predictor candidate list, and may determine motion information of the target block based on the derived motion vector predictor candidates.

The decoding apparatus 200 may determine a motion vector candidate for the target block from among the predicted motion vector candidates included in the predicted motion vector candidate list using the predicted motion vector index. The decoding apparatus 200 may select the motion vector predictor candidate indicated by the motion vector predictor index from among the motion vector predictor candidates included in the motion vector predictor candidate list as the motion vector predictor of the target block.

The motion vector that will actually be used for inter prediction of the target block may not match the predicted motion vector. In order to indicate the difference between the motion vector that will actually be used for inter-predicting the target block and the predicted motion vector, MVD may be used. The encoding apparatus 100 may derive a predicted motion vector similar to the motion vector actually to be used for inter prediction of the target block, so as to use the MVD as small as possible.

The MVD may be the difference between the motion vector of the target block and the predicted motion vector. The encoding apparatus 100 may calculate the MVD, and may perform entropy encoding on the MVD.

The MVD may be transmitted from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream. The decoding apparatus 200 may decode the received MVD. The decoding apparatus 200 may derive the motion vector of the target block by summing the decoded MVD and the predicted motion vector. In other words, the motion vector of the target block derived by the decoding apparatus 200 may be the sum of the entropy decoded MVD and the motion vector candidates.

The reference direction may indicate a list of reference pictures to be used for prediction of the target block. For example, the reference direction may indicate one of the reference picture list L0 and the reference picture list L1.

The reference direction only indicates a list of reference pictures to be used for prediction of the target block, and may not mean that the direction of the reference pictures is limited to the forward direction or the backward direction. In other words, each of the reference picture list L0 and the reference picture list L1 may include pictures in the forward direction and/or the backward direction.

The reference direction being unidirectional may mean using a single reference picture list. The reference direction being bidirectional may mean using two reference picture lists. In other words, the reference direction may indicate one of the following cases: a case where only the reference picture list L0 is used, a case where only the reference picture list L1 is used, and a case where two reference picture lists are used.

The reference picture index may indicate a reference picture to be used for prediction of the target block among the reference pictures in the reference picture list. The reference picture index may be entropy encoded by the encoding apparatus 100 . The entropy-encoded reference picture index may be signaled by the encoding apparatus 100 to the decoding apparatus 200 through a bitstream.

When two reference picture lists are used to predict the target block, a single reference picture index and a single motion vector may be used for each of the reference picture lists. Also, when two reference picture lists are used to predict the target block, two prediction blocks may be designated for the target block. For example, the average or weighted sum of the two predicted blocks for the target block may be used to generate the (final) predicted block of the target block.

The motion vector of the target block may be derived through the predicted motion vector index, MVD, reference direction, and reference picture index.

The decoding apparatus 200 may generate a prediction block for the target block based on the derived motion vector and the reference picture index. For example, the prediction block may be the reference block indicated by the derived motion vector in the reference picture indicated by the reference picture index.

Since the predicted motion vector index and the MVD are encoded while the motion vector of the target block itself is not encoded, the number of bits transmitted from the encoding apparatus 100 to the decoding apparatus 200 can be reduced, and encoding efficiency can be improved.

The motion information of the reconstructed neighboring blocks may be used for the target block. In a specific inter prediction mode, the encoding apparatus 100 may not separately encode the actual motion information of the target block. The motion information of the target block is not encoded, but additional information may be encoded, wherein the additional information enables the motion information of the target block to be derived using the motion information of the reconstructed neighboring blocks. Since the additional information is encoded, the number of bits transmitted to the decoding apparatus 200 can be reduced, and encoding efficiency can be improved.

For example, as an inter prediction mode in which the motion information of the target block is not directly encoded, there may be a skip mode and/or a merge mode. Here, each of the encoding apparatus 100 and the decoding apparatus 200 may use an indicator and/or an index indicating a unit whose motion information is to be used as the motion information of the target unit among reconstructed neighboring units.

2) Merge mode

As a scheme for deriving motion information of a target block, there is merging. The term "merging" may mean merging the motions of multiple blocks. "Merge" may mean that the motion information of one block is also applied to other blocks. In other words, the merge mode may be a mode in which the motion information of the target block is derived from the motion information of the neighboring blocks.

When the merge mode is used, the encoding apparatus 100 may predict the motion information of the target block using the motion information of the spatial candidate and/or the motion information of the temporal candidate. The spatial candidates may include reconstructed spatially neighboring blocks that are spatially adjacent to the target block. The spatial neighboring blocks may include left neighboring blocks and upper neighboring blocks. Temporal candidates may include col blocks. The terms "spatial candidate" and "spatial merging candidate" may be used to have the same meaning and may be used interchangeably with each other. The terms "temporal candidate" and "temporal merge candidate" may be used to have the same meaning and may be used interchangeably with each other.

The encoding apparatus 100 may obtain a prediction block through prediction. The encoding apparatus 100 may encode the residual block, which is the difference between the target block and the prediction block.

2-1) Create a merge candidate list

When the merge mode is used, each of the encoding apparatus 100 and the decoding apparatus 200 may create a merge candidate list using motion information of spatial candidates and/or motion information of temporal candidates. The motion information may include 1) a motion vector, 2) a reference picture index, and 3) a reference direction. The reference direction can be unidirectional or bidirectional.

The merge candidate list may include merge candidates. Merge candidates may be motion information. In other words, the merging candidate list may be a list storing a plurality of pieces of motion information.

The merging candidates may be pieces of motion information of temporal candidates and/or spatial candidates. Also, the merge candidate list may include new merge candidates generated by combining merge candidates already existing in the merge candidate list. In other words, the merge candidate list may include new motion information generated by combining pieces of motion information previously existing in the merge candidate list.

A merge candidate may be a specific mode in which inter prediction information is derived. The merge candidate may be information indicating a specific mode of deriving inter prediction information. The inter prediction information of the target block may be derived according to the specific mode indicated by the merge candidate. Furthermore, the specific mode may include a process of deriving a series of inter prediction information. This specific mode may be an inter prediction information derivation mode or a motion information derivation mode.

The inter prediction information of the target block may be derived according to the mode indicated by the merge candidate selected from among the merge candidates in the merge candidate list by the merge index.

For example, the motion information derivation mode in the merge candidate list may be at least one of the following modes: 1) a motion information derivation mode for sub-block units; 2) an affine motion information derivation mode. Also, the merge candidate list may include motion information of the zero vector. A zero vector may also be referred to as a "zero merge candidate".

In other words, the pieces of motion information in the merge candidate list may be at least one of the following information: 1) motion information of spatial candidates, 2) motion information of temporal candidates, 3) motion information of Motion information generated by combining a plurality of pieces of motion information, and 4) a zero vector.

The motion information may include 1) a motion vector, 2) a reference picture index, and 3) a reference direction. The reference direction may also be referred to as an "inter prediction indicator". The reference direction can be unidirectional or bidirectional. A unidirectional reference direction may indicate L0 prediction or L1 prediction.

A merge candidate list may be created before prediction in merge mode is performed.

The number of merge candidates in the merge candidate list may be predefined. Each of the encoding apparatus 100 and the decoding apparatus 200 may add merging candidates to the merging candidate list according to a predefined scheme and a predefined priority so that the merging candidate list has a predefined number of merging candidates. The merging candidate list of the encoding apparatus 100 and the merging candidate list of the decoding apparatus 200 may be made identical to each other using a predefined scheme and a predefined priority.

Merging may be applied on a CU or PU basis. When combining is performed on a CU or PU basis, the encoding apparatus 100 may transmit a bitstream including predefined information to the decoding apparatus 200 . For example, the predefined information may include 1) information indicating whether or not to perform merging for each block partition, and 2) information on blocks to be merged among blocks that are spatial candidates and/or temporal candidates for the target block block information.

2-2) Search motion vector using merge candidate list

The encoding apparatus 100 may determine merge candidates to be used for encoding the target block. For example, the encoding apparatus 100 may perform prediction on the target block using the merge candidates in the merge candidate list, and may generate a residual block for the merge candidates. The encoding apparatus 100 may encode the target block using a merge candidate that generates the least cost in encoding of prediction and residual blocks.

Also, the encoding apparatus 100 may determine whether to encode the target block using the merge mode.

2-3) Transmission of inter-frame prediction information

The encoding apparatus 100 may generate a bitstream including inter prediction information required for inter prediction. The encoding apparatus 100 may generate entropy-encoded inter-prediction information by performing entropy encoding on the inter-prediction information, and may transmit a bitstream including the entropy-encoded inter-prediction information to the decoding apparatus 200 . The entropy-encoded inter prediction information may be signaled by the encoding apparatus 100 to the decoding apparatus 200 through a bitstream.

The decoding apparatus 200 may perform inter prediction on the target block using the inter prediction information of the bitstream.

The inter prediction information may include 1) mode information indicating whether a merge mode is used and 2) a merge index.

Furthermore, the inter prediction information may include residual signals.

The decoding apparatus 200 may acquire the merge index from the bitstream only when the mode information indicates that the merge mode is used.

The mode information may be a merge flag. The unit of mode information may be a block. The information about the block may include mode information, and the mode information may indicate whether the merge mode is applied to the block.

The merge index may indicate a merge candidate to be used for prediction of the target block among the merge candidates included in the merge candidate list. Alternatively, the merge index may indicate a block to be merged with the target block among neighboring blocks that are spatially or temporally adjacent to the target block.

The encoding apparatus 100 may select the merge candidate with the highest encoding performance among the merge candidates included in the merge candidate list, and set the value of the merge index to indicate the selected merge candidate.

2-4) Inter prediction of merge mode using inter prediction information

The decoding apparatus 200 may perform prediction on the target block using the merging candidate indicated by the merging index among the merging candidates included in the merging candidate list.

The motion vector of the target block may be specified by the motion vector of the merge candidate indicated by the merge index, the reference picture index, and the reference direction.

3) Skip mode

The skip mode may be a mode in which motion information of a spatial candidate or motion information of a temporal candidate is applied to the target block without change. Also, the skip mode may be a mode in which the residual signal is not used. In other words, when the skip mode is used, the reconstructed block may be the predicted block.

The difference between merge mode and skip mode is whether a residual signal is sent or used. That is, skip mode may be similar to merge mode, except that no residual signal is sent or used.

When the skip mode is used, the encoding apparatus 100 may transmit, to the decoding apparatus 200 through a bitstream, information about a block whose motion information is to be used as the motion information of the target block among the blocks that are spatial candidates or temporal candidates . The encoding apparatus 100 may generate entropy-encoded information by performing entropy encoding on the information, and may signal the entropy-encoded information to the decoding apparatus 200 through a bitstream.

Also, when the skip mode is used, the encoding apparatus 100 may not transmit other syntax information such as MVD to the decoding apparatus 200 . For example, when the skip mode is used, the encoding apparatus 100 may not signal syntax elements related to at least one of MVC, encoding block flags, and transform coefficient levels to the decoding apparatus 200 .

3-1) Create a merge candidate list

The skip mode can also use a merge candidate list. In other words, the merge candidate list can be used in both merge mode and skip mode. In this regard, the merge candidate list may also be referred to as a "skip candidate list" or a "merge/skip candidate list".

Optionally, skip mode may use an additional candidate list that is different from that of merge mode. In this case, in the following description, the merge candidate list and the merge candidate may be replaced with a skip candidate list and a skip candidate, respectively.

A merge candidate list may be created before prediction in skip mode is performed.

3-2) Search motion vector using merge candidate list

The encoding apparatus 100 may determine merge candidates to be used for encoding the target block. For example, the encoding apparatus 100 may perform prediction on the target block using merge candidates in the merge candidate list. The encoding apparatus 100 may encode the target block using a merge candidate that generates the least cost in prediction.

Also, the encoding apparatus 100 may determine whether to encode the target block using the skip mode.

3-3) Transmission of inter-frame prediction information

The encoding apparatus 100 may generate a bitstream including inter prediction information required for inter prediction. The decoding apparatus 200 may perform inter prediction on the target block using the inter prediction information of the bitstream.

The inter prediction information may include 1) mode information indicating whether a skip mode is used and 2) a skip index.

The skip index may be the same as the merge index described above.

When using skip mode, the target block can be encoded without using a residual signal. The inter prediction information may not include residual signals. Alternatively, the bitstream may not include a residual signal.

The decoding apparatus 200 may acquire the skip index from the bitstream only when the mode information indicates that the skip mode is used. As described above, the merge index and the skip index may be the same as each other. The decoding apparatus 200 may acquire the skip index from the bitstream only when the mode information indicates that the merge mode or the skip mode is used.

The skip index may indicate a merging candidate to be used for prediction of the target block among the merging candidates included in the merging candidate list.

3-4) Inter prediction in skip mode using inter prediction information

The decoding apparatus 200 may perform prediction on the target block using the merge candidate indicated by the skip index among the merge candidates included in the merge candidate list.

The motion vector of the target block may be specified by the motion vector of the merge candidate indicated by the skip index, the reference picture index, and the reference direction.

4) Current screen reference mode

The current picture reference mode may represent a prediction mode that uses a previously reconstructed region in the target picture to which the target block belongs.

Motion vectors that specify previously reconstructed regions can be used. The reference picture index of the target block may be used to determine whether the target block has been encoded in the current picture reference mode.

A flag or index indicating whether the target block is a block encoded in the current picture reference mode may be signaled by the encoding apparatus 100 to the decoding apparatus 200 . Alternatively, whether the target block is a block encoded in the current picture reference mode may be inferred from the reference picture index of the target block.

When the target block is encoded in the current picture reference mode, the current picture may exist at a fixed position or an arbitrary position in the reference picture list for the target block.

For example, the fixed position may be the position where the reference picture index is 0 or the last position.

When a target picture exists at an arbitrary position in the reference picture list, an additional reference picture index indicating such an arbitrary position may be signaled by the encoding apparatus 100 to the decoding apparatus 200 .

In the AMVP mode, merge mode, and skip mode described above, motion information to be used for prediction of a target block among pieces of motion information in the list may be specified using an index of the list.

In order to improve encoding efficiency, the encoding apparatus 100 may signal only an index of an element that generates a minimum cost in inter prediction on the target block among the elements in the list. The encoding apparatus 100 may encode the index, and may signal the encoded index.

Therefore, it must be possible to derive the above-described lists (ie, the motion vector predictor candidate list and the merge candidate list) based on the same data using the same scheme by the encoding apparatus 100 and the decoding apparatus 200 . Here, the same data may include reconstructed pictures and reconstructed blocks. Also, in order to specify an element using an index, the order of the elements in the list must be fixed.

FIG. 10 shows spatial candidates according to an embodiment.

In Fig. 10, the positions of the spatial candidates are shown.

The large block at the center of the graph may represent the target block. Five tiles can represent spatial candidates.

The coordinates of the target block can be (xP, yP), and the size of the target block can be represented by (nPSW, nPSH).

The spatial candidate A ₀ may be a block adjacent to the lower left corner of the target block. A ₀ may be a block occupying the pixel located at coordinates (xP-1, yP+nPSH+1).

_The spatial coordinate A1 may be the block adjacent to the left of the target block. A ₁ may be the lowermost block among the blocks adjacent to the left of the target block. Alternatively, A1 may be the block adjacent to the top _{of A0} . A1 may be _a block occupying the pixel located at coordinates (xP-1, yP+nPSH).

The spatial candidate B ₀ may be a block adjacent to the upper right corner of the target block. B ₀ may be a block occupying the pixel located at coordinates (xP+nPSW+1, yP-1).

The spatial candidate B1 may be _a block adjacent to the top of the target block. B ₁ may be the rightmost block among the blocks adjacent to the top of the target block. Alternatively, B1 may be the block adjacent to the left _{of B0} . B ₁ may be a block occupying the pixel located at coordinates (xP+nPSW, yP-1).

The spatial candidate B2 may be a block adjacent to the upper left corner of the target block. B2 may be a block occupying the pixel located at coordinates (xP-1, yP-1).

Determination of availability of spatial and temporal candidates

In order to include the motion information of the spatial candidate or the motion information of the temporal candidate in the list, it must be determined whether the motion information of the spatial candidate or the motion information of the temporal candidate is available.

Hereinafter, candidate blocks may include spatial candidates and temporal candidates.

For example, the determination may be performed by sequentially applying the following steps 1) to 4).

Step 1) When the PU including the candidate block is located outside the boundary of the picture, the availability of the candidate block may be set to "false". The expression "availability is set to false" may have the same meaning as "set to unavailable".

Step 2) When the PU including the candidate block is located outside the boundary of the slice, the availability of the candidate block may be set to "false". When the target block and the candidate block are located in different slices, the availability of the candidate block may be set to "false".

Step 3) When the PU including the candidate block is located outside the boundary of the parallel block, the availability of the candidate block may be set to "false". When the target block and the candidate block are located in different parallel blocks, the availability of the candidate block may be set to "false".

Step 4) When the prediction mode of the PU including the candidate block is the intra prediction mode, the availability of the candidate block may be set to "false". When the PU including the candidate block does not use inter prediction, the availability of the candidate block may be set to "false".

FIG. 11 illustrates an order of adding motion information of spatial candidates to a merge list according to an embodiment.

As shown in FIG. 11 , when pieces of motion information of spatial candidates are added to the merge list, the order of A ₁ , B ₁ , B ₀ , A ₀ , and B ₂ may be used. That is, pieces of motion information of available space candidates may be added to the merge list in the order of A ₁ , B ₁ , B ₀ , A ₀ , and B ₂ .

Methods for deriving merged lists in merge mode and skip mode

As described above, the maximum number of merge candidates in the merge list can be set. "N" can be used to indicate the maximum number of settings. The set number may be transmitted from the encoding apparatus 100 to the decoding apparatus 200 . The strip header of the strip may include N. In other words, the maximum number of merge candidates in the merge list for the target block of the slice can be set by the slice header. For example, the value of N can be substantially 5.

A plurality of pieces of motion information (ie, merge candidates) may be added to the merge list in the order of steps 1) to 4) below.

Step 1) Among the space candidates, the available space candidates may be added to the merged list. The pieces of motion information of the available space candidates may be added to the merge list in the order shown in FIG. 10 . Here, when the motion information of the available space candidates overlaps with other motion information already existing in the merge list, the motion information of the available space candidates may not be added to the merge list. The operation of checking whether the corresponding motion information overlaps with other motion information existing in the list may be simply referred to as "overlap checking".

The maximum number of pieces of motion information to be added may be N.

Step 2) When the number of pieces of motion information in the merge list is less than N and the temporal candidates are available, the motion information of the temporal candidates can be added to the merge list. Here, when the motion information of the available temporal candidates overlaps with other motion information already existing in the merge list, the motion information of the temporal candidates may not be added to the merge list.

Step 3) When the number of pieces of motion information in the merge list is less than N and the type of the target slice is "B", the combined motion information generated by combined bidirectional prediction (bi-prediction) may be added to the merge list.

The target slice may be a slice including target blocks.

The combined motion information may be a combination of L0 motion information and L1 motion information. The L0 motion information may be motion information referring only to the reference picture list L0. The L1 motion information may be motion information referring only to the reference picture list L1.

In the merged list, there may be one or more pieces of L0 motion information. Also, in the merged list, there may be one or more pieces of L1 motion information.

The combined motion information may include one or more pieces of combined motion information. When generating combined motion information, L0 motion information and L1 to be used in the step of generating combined motion information among the one or more pieces of L0 motion information and the one or more pieces of L1 motion information may be predefined sports information. One or more pieces of combined motion information may be generated in a predefined order via bidirectional prediction using a combination of a pair of different motion information in the merged list. One piece of motion information in the pair of different motion information may be L0 motion information, and the other piece of motion information in the pair of different motion information may be L1 motion information.

For example, the combined motion information added with the highest priority may be a combination of L0 motion information with merge index 0 and L1 motion information with merge index 1. When motion information with merge index 0 is not L0 motion information or when motion information with merge index 1 is not L1 motion information, combined motion information may neither be generated nor added. Next, the combined motion information added with the next priority may be a combination of L0 motion information with merge index 1 and L1 motion information with merge index 0. The detailed combinations that follow may conform to other combinations in the field of video encoding/decoding.

Here, when the combined motion information overlaps with other motion information already existing in the merge list, the combined motion information may not be added to the merge list.

Step 4) When the number of pieces of motion information in the merge list is less than N, the motion information of the zero vector can be added to the merge list.

The zero vector motion information may be motion information in which the motion vector is a zero vector.

The number of pieces of zero vector motion information may be one or more. The reference picture indices of one or more pieces of zero vector motion information may be different from each other. For example, the value of the reference picture index of the first zero vector motion information may be 0. The value of the reference picture index of the second zero vector motion information may be 1.

The number of pieces of zero vector motion information may be the same as the number of reference pictures in the reference picture list.

The reference direction of the zero vector motion information can be bidirectional. The two motion vectors can be zero vectors. The number of pieces of zero vector motion information may be the smaller one of the number of reference pictures in the reference picture list L0 and the number of reference pictures in the reference picture list L1. Alternatively, when the number of reference pictures in the reference picture list L0 and the number of reference pictures in the reference picture list L1 are different from each other, a reference direction that is a unidirectional can be used for a reference that can only be applied to a single reference picture list screen index.

The encoding apparatus 100 and/or the decoding apparatus 200 may then add the zero vector motion information to the merge list while changing the reference picture index.

When the zero vector motion information overlaps with other motion information already present in the merge list, the zero vector motion information may not be added to the merge list.

The order of the above steps 1) to 4) is only exemplary and may be changed. Furthermore, some of the above steps may be omitted according to predefined conditions.

Method for deriving motion vector predictor candidate list in AMVP mode

The maximum number of motion vector predictor candidates in the motion vector predictor candidate list may be predefined. N can be used to indicate a predefined maximum number. For example, the predefined maximum number can be 2.

A plurality of pieces of motion information (ie, motion vector predictor candidates) may be added to the motion vector predictor candidate list in the order of step 1) to step 3) below.

Step 1) The available spatial candidates among the spatial candidates may be added to the predicted motion vector candidate list. The spatial candidates may include a first spatial candidate and a second spatial candidate.

The first spatial candidate may be one of A ₀ , A ₁ , scaled A ₀ , and scaled A ₁ . The second spatial candidate may be one of B ₀ , B ₁ , B ₂ , scaled B ₀ , scaled B ₁ , and scaled B ₂ .

The pieces of motion information of the available spatial candidates may be added to the motion vector predictor candidate list in the order of the first spatial candidate and the second spatial candidate. In this case, when the motion information of the available space candidates overlaps with other motion information already existing in the motion vector predictor candidate list, the motion information of the available space candidates may not be added to the motion vector predictor candidate list. In other words, when the value of N is 2, if the motion information of the second spatial candidate is the same as that of the first spatial candidate, the motion information of the second spatial candidate may not be added to the motion vector predictor candidate list.

The maximum number of pieces of motion information to be added may be N.

Step 2) When the number of pieces of motion information in the motion vector predictor candidate list is less than N and the temporal candidates are available, the motion information of the temporal candidates may be added to the motion vector predictor candidate list. In this case, when the motion information of the available temporal candidates overlaps with other motion information already existing in the motion vector predictor candidate list, the motion information of the available temporal candidates may not be added to the motion vector predictor candidate list.

Step 3) When the number of pieces of motion information in the motion vector predictor candidate list is less than N, zero vector motion information may be added to the motion vector predictor candidate list.

The zero vector motion information may include one or more pieces of zero vector motion information. The reference picture indices of the one or more pieces of zero vector motion information may be different from each other.

The encoding apparatus 100 and/or the decoding apparatus 200 may sequentially add pieces of zero vector motion information to the predicted motion vector candidate list while changing the reference picture index.

When the zero vector motion information overlaps with other motion information already present in the motion vector predictor candidate list, the zero vector motion information may not be added to the motion vector predictor candidate list.

The description of the zero vector motion information made above in connection with the merge list can also be applied to the zero vector motion information. Duplicate descriptions thereof will be omitted.

The order of step 1) to step 3) described above is only exemplary and may be changed. Furthermore, some of the steps may be omitted according to predefined conditions.

Figure 12 shows transform and quantization processing according to an example.

As shown in FIG. 12, the quantized levels may be generated by performing transform and/or quantization processing on the residual signal.

The residual signal may be generated as the difference between the original block and the predicted block. Here, the prediction block may be a block generated via intra prediction or inter prediction.

The residual signal may be transformed into a signal in the frequency domain by a transformation process as part of the quantization process.

Transform kernels for transforms may include various DCT kernels, such as discrete cosine transform (DCT) type 2 (DCT-II) and discrete sine transform (DST) kernels.

These transform kernels can perform a separable transform or a two-dimensional (2D) non-separable transform on the residual signal. The separable transform may be a transform indicating that a one-dimensional (1D) transform is performed on the residual signal in each of the horizontal and vertical directions.

The DCT types and DST types adaptively used for the 1D transform may include DCT-V, DCT-VIII, DST-I, and DST-VII in addition to DCT-II, as shown in Table 3 below.

table 3

transform set Transform candidates 0 DST-VII, DCT-VIII 1 DST-VII, DST-I 2 DST-VII, DCT-V

As shown in Table 3, when the DCT type or DST type to be used for the transform is deduced, the transform set can be used. Each transform set may include multiple transform candidates. Each transform candidate may be of DCT type or DST type.

Table 4 below shows an example of transform sets applied to the horizontal direction according to intra prediction modes.

Table 4

In Table 4, the number of each transform set to be applied to the horizontal direction of the residual signal is indicated according to the intra prediction mode of the target block.

Table 5 below shows an example of a transform set applied to the vertical direction of the residual signal according to the intra prediction mode.

table 5

As exemplified in Tables 4 and 5, transform sets to be applied to the horizontal and vertical directions may be predefined according to the intra prediction mode of the target block. The encoding apparatus 100 may perform transform and inverse transform on the residual signal using the transform included in the transform set corresponding to the intra prediction mode of the target block. Also, the decoding apparatus 200 may perform inverse transform on the residual signal using the transform included in the transform set corresponding to the intra prediction mode of the target block.

In transform and inverse transform, as exemplified in Table 3, Table 4, and Table 5, the set of transforms to be applied to the residual signal may be determined, and may not be signaled. The transformation indication information may be signaled from the encoding apparatus 100 to the decoding apparatus 200 . The transform indication information may be information indicating which of a plurality of transform candidates included in the transform set to be applied to the residual signal is used.

As described above, methods using various transforms may be applied to residual signals generated via intra prediction or inter prediction.

The transformation may include at least one of a first transformation and a second transformation. The transform coefficients may be generated by performing a first transform on the residual signal, and the second transform coefficients may be generated by performing a second transform on the transform coefficients.

The first transformation may be referred to as the "main transformation". Furthermore, the first transform may also be referred to as an "adaptive multi-transform (AMT) scheme". As described above, AMT may represent applying different transforms to each 1D direction (ie, vertical and horizontal).

The secondary transform may be a transform for increasing the energy concentration of the transform coefficients generated by the first transform. Similar to the first transform, the second transform can be a separable transform or a non-separable transform. Such a non-separable transform may be a non-separable quadratic transform (NSST).

The first transformation may be performed using at least one of a number of predefined transformation methods. For example, the predefined multiple transform methods may include discrete cosine transform (DCT), discrete sine transform (DST), Karhunen-Loeve transform (KLT), and the like.

The second transform may be performed on the transform coefficients generated by performing the first transform.

The first transform and the second transform may be applied to signal components corresponding to one or more of a luma (luma) component and a chroma (chroma) component. Whether to apply the primary transform and/or the secondary transform may be determined according to at least one of encoding parameters for the target block and/or neighboring blocks. For example, whether to apply the primary transform and/or the secondary transform may be determined according to the size and/or shape of the target block.

The transform method to be applied to the first transform and/or the second transform may be determined according to at least one of encoding parameters for the target block and/or neighboring blocks. The determined transform method may also indicate that the first transform and/or the second transform is not used.

Alternatively, transform information indicating the transform method may be signaled from the encoding apparatus 100 to the decoding apparatus 200 . For example, the transform information may include indices of transforms to be used for the first transform and/or the second transform.

The level of quantization may be generated by performing quantization on the result generated by performing the first transform and/or the second transform, or by performing quantization on the residual signal.

Figure 13 shows a diagonal scan according to an example.

FIG. 14 shows horizontal scanning according to an example.

FIG. 15 shows vertical scanning according to an example.

The quantized transform coefficients may be scanned via (top right) at least one of diagonal scanning, vertical scanning, and horizontal scanning according to at least one of intra prediction mode, block size, and block shape. The block may be a transform unit (TU)

Each scan can start at a specific start point and can end at a specific end point.

For example, the quantized transform coefficients may be changed into 1D vector form by scanning the coefficients of the block using the diagonal scanning of FIG. 13 . Alternatively, the horizontal scan of FIG. 14 or the vertical scan of FIG. 15 may be used instead of the diagonal scan according to the size of the block and/or the intra prediction mode.

Vertical scanning may be an operation of scanning 2D block type coefficients in the column direction. Horizontal scanning may be an operation of scanning 2D block type coefficients in the row direction.

In other words, which of the diagonal scan, the vertical scan and the horizontal scan will be used may be determined according to the size of the block and/or the inter prediction mode.

As shown in FIGS. 13 , 14 and 15 , the quantized transform coefficients may be scanned in a diagonal direction, a horizontal direction, or a vertical direction.

The quantized transform coefficients may be represented by a block shape. Each block may include multiple sub-blocks. Each sub-block may be defined according to a minimum block size or minimum block shape.

In scanning, a scanning order according to the type or direction of scanning may be applied to the sub-blocks first. Also, a scanning order according to the direction of scanning may be applied to the quantized transform coefficients in each sub-block.

For example, as shown in FIGS. 13 , 14 and 15 , when the size of the target block is 8×8, quantized transform coefficients may be generated by first transforming, second transforming, and quantizing the residual signal of the target block . Thus, one of three types of scan orders can be applied to the four 4x4 sub-blocks, and the quantized transform coefficients can also be scanned for each 4x4 sub-block according to the scan order.

The scanned quantized transform coefficients may be entropy encoded, and the bitstream may include the entropy encoded quantized transform coefficients.

The decoding apparatus 200 may generate quantized transform coefficients via entropy decoding of the bitstream. The quantized transform coefficients may be arranged in 2D blocks via inverse scanning. Here, as a method of inverse scanning, at least one of upper-right diagonal scanning, vertical scanning, and horizontal scanning may be performed.

Inverse quantization may be performed on the quantized transform coefficients. The result generated by performing inverse quantization may be subjected to inverse quadratic transformation according to whether or not inverse quadratic transformation is performed. Also, the first inverse transformation may be performed on the result generated by performing the second inverse transformation according to whether the first inverse transformation will be performed. The reconstructed residual signal may be generated by performing a first inverse transform on a result generated by performing a second inverse transform.

FIG. 16 is a configuration diagram of an encoding apparatus according to an embodiment.

The encoding apparatus 1600 may correspond to the encoding apparatus 100 described above.

The encoding apparatus 1600 may include a processing unit 1610, a memory 1630, a user interface (UI) input device 1650, a UI output device 1660, and a memory 1640 in communication with each other through a bus 1690. The electronic device 1600 may also include a communication unit 1620 connected to the network 1699 .

The processing unit 1610 may be a central processing unit (CPU) or a semiconductor device for executing processing instructions stored in the memory 1630 or the memory 1640 . The processing unit 1610 may be at least one hardware processor.

The processing unit 1610 may generate and process signals, data, or information input to the encoding apparatus 1600, output from the encoding apparatus 1600, or used in the encoding apparatus 1600, and may perform inspection, comparison on the signals, data, or information , OK, etc. In other words, in an embodiment, the generation and processing of data or information and the checking, comparison and determination of data or information may be performed by the processing unit 1610 .

The processing unit 1610 may include an inter prediction unit 110, an intra prediction unit 120, a switch 115, a subtractor 125, a transform unit 130, a quantization unit 140, an entropy encoding unit 150, an inverse quantization unit 160, an inverse transform unit 170, an adder 175 , filter unit 180 and reference picture buffer 190 .

Inter prediction unit 110, intra prediction unit 120, switch 115, subtractor 125, transform unit 130, quantization unit 140, entropy encoding unit 150, inverse quantization unit 160, inverse transform unit 170, adder 175, filter unit At least some of 180 and reference picture buffer 190 may be program modules and may communicate with an external device or system. The program modules may be included in the encoding device 1600 in the form of an operating system, application program modules, or other program modules.

The program modules may be physically stored in various types of well-known storage devices. Furthermore, at least some of the program modules may also be stored in a remote storage device capable of communicating with the encoding apparatus 1200 .

Program modules may include, but are not limited to, routines, subroutines, programs, objects, components, and data structures for performing functions or operations according to embodiments or for implementing abstract data types according to embodiments.

The program modules may be implemented using instructions or code executed by at least one processor of the encoding device 1600 .

Processing unit 1610 may operate inter prediction unit 110, intra prediction unit 120, switch 115, subtractor 125, transform unit 130, quantization unit 140, entropy encoding unit 150, inverse quantization unit 160, inverse transform unit 170, adders 175 , the filter unit 180 and the instructions or code in the reference picture buffer 190 .

The storage unit may represent memory 1630 and/or storage 1640 . Each of memory 1630 and storage 1640 may be any of various types of volatile or nonvolatile storage media. For example, the memory 1630 may include at least one of a read only memory (ROM) 1631 and a random access memory (RAM) 1632 .

The storage unit may store data or information used for the operation of the encoding apparatus 1600 . In an embodiment, the data or information of the encoding apparatus 1600 may be stored in a storage unit.

For example, the storage unit may store pictures, blocks, lists, motion information, inter prediction information, bitstreams, and the like.

The encoding apparatus 1600 may be implemented in a computer system including a computer-readable storage medium.

The storage medium may store at least one module required for the operation of the encoding apparatus 1600 . The memory 1630 may store at least one module and may be configured such that the at least one module is executed by the processing unit 1610 .

Functions related to communication of data or information of the encoding apparatus 1600 may be performed through the communication unit 1620 .

For example, the communication unit 1620 may transmit the bitstream to the decoding apparatus 1600 which will be described later.

FIG. 17 is a configuration diagram of a decoding apparatus according to an embodiment.

The decoding apparatus 1700 may correspond to the decoding apparatus 200 described above.

The decoding apparatus 1700 may include a processing unit 1710, a memory 1730, a user interface (UI) input device 1750, a UI output device 1760, and a memory 1740 in communication with each other through a bus 1790. The decoding device 1700 may also include a communication unit 1720 connected to the network 1799 .

The processing unit 1710 may be a central processing unit (CPU) or a semiconductor device for executing processing instructions stored in the memory 1730 or the memory 1740 . The processing unit 1710 may be at least one hardware processor.

The processing unit 1710 may generate and process signals, data or information input to the decoding apparatus 1700, output from the decoding apparatus 1700, or used in the decoding apparatus 1700, and may perform checking, comparison related to the signals, data or information , OK, etc. In other words, in an embodiment, the generation and processing of data or information and the checking, comparison and determination of data or information may be performed by the processing unit 1710 .

The processing unit 1710 may include an entropy decoding unit 210 , an inverse quantization unit 220 , an inverse transform unit 230 , an intra prediction unit 240 , an inter prediction unit 250 , a switch 245 , an adder 255 , a filter unit 260 , and a reference picture buffer 270 .

In the entropy decoding unit 210 , the inverse quantization unit 220 , the inverse transform unit 230 , the intra prediction unit 240 , the inter prediction unit 250 , the adder 255 , the switch 245 , the filter unit 260 and the reference picture buffer 270 of the decoding apparatus 200 At least some of the modules may be program modules and may communicate with external devices or systems. The program modules may be included in the decoding device 1700 in the form of an operating system, application program modules, or other program modules.

Program modules may be physically stored in various types of well-known storage devices. Furthermore, at least some of the program modules may also be stored in a remote storage device capable of communicating with the decoding apparatus 1700 .

Program modules may include, but are not limited to, routines, subroutines, programs, objects, components, and data structures for performing functions or operations according to embodiments or for implementing abstract data types according to embodiments.

The program modules may be implemented using instructions or code executed by at least one processor of the decoding apparatus 1700 .

Processing unit 1710 may operate entropy decoding unit 210 , inverse quantization unit 220 , inverse transform unit 230 , intra prediction unit 240 , inter prediction unit 250 , switch 245 , adder 255 , filter unit 260 , and reference picture buffer 270 instruction or code in .

The storage unit may represent memory 1730 and/or storage 1740 . Each of memory 1730 and storage 1740 may be any of various types of volatile or non-volatile storage media. For example, the memory 1730 may include at least one of the ROM 1731 and the RAM 1732 .

The storage unit may store data or information for the operation of the decoding apparatus 1700 . In an embodiment, the data or information of the decoding apparatus 1700 may be stored in a storage unit.

For example, the storage unit may store pictures, blocks, lists, motion information, inter prediction information, bitstreams, and the like.

The decoding apparatus 1700 may be implemented in a computer system including a computer-readable storage medium.

The storage medium may store at least one module required for the operation of the decoding apparatus 1700 . The memory 1730 may store at least one module and may be configured such that the at least one module is executed by the processing unit 1710 .

Functions related to communication of data or information of the decoding apparatus 1700 may be performed through the communication unit 1720 .

For example, the communication unit 1720 may receive the bitstream from the encoding apparatus 1600 .

Method and apparatus for bidirectional intra prediction

18 is a flowchart of a bidirectional intra prediction method according to an embodiment.

The bidirectional intra prediction method may be performed by the encoding apparatus 1600 and/or the decoding apparatus 1700 .

For example, the encoding apparatus 1600 may perform the prediction method according to the embodiment in order to compare the efficiencies of the various prediction methods for the target block and/or the plurality of partition blocks, and may also perform the prediction method according to the embodiment in order to generate the prediction method for the target block and/or the plurality of partition blocks. The reconstructed block of the target block.

In an embodiment, the target block may be a PU, or may be at least one of a CTB, a CU, a PU, a TU, a sub-block, a block with a certain size, and a block with a size within a predefined range. Alternatively, the target block may be an encoded unit.

For example, the decoding apparatus 1700 may perform the prediction method according to the embodiment in order to generate a reconstructed block for the target block.

Hereinafter, the term "processing unit" may correspond to the processing unit 1610 of the encoding apparatus 1600 and/or the processing unit 1710 of the decoding apparatus 1700.

At step 1810, the processing unit may determine a bidirectional intra prediction mode to be applied to encoding and/or decoding of the target block.

The processing unit may determine and derive a bidirectional intra prediction mode based on at least one of: 1) an intra prediction mode indicator, 2) a unidirectional/bidirectional classification indicator, 3) a most probable mode (MPM), 4) located at Availability of pixels in neighboring blocks in the specified direction of the target block, and 5) prediction modes of neighboring blocks.

At step 1820, the processing unit may determine a prediction value for a prediction block of the target block by performing bidirectional intra prediction on the target block using the determined bidirectional intra prediction mode.

In an embodiment, the two directions of bidirectional intra prediction may be two linear directions implemented in opposite directions. For example, the two directions may be a direction at an angle of 45° and a direction at an angle of 225°.

In an embodiment, the two directions of bidirectional intra prediction may be two different directions that are not oriented collinearly. For example, the two directions may be a direction at an angle of 45° and a direction at an angle of 90°.

The processing unit may generate at least one virtual neighboring pixel in the specified direction of the target block, and may perform bidirectional intra prediction for the target block using the at least one virtual neighboring pixel. The processing unit may derive a prediction value for the target pixel in the prediction block based on the at least one virtual neighboring pixel. The specified direction may include one or more of a right direction and a downward direction.

The target pixel may be a pixel that is the target of encoding and/or decoding.

The processing unit may derive the predicted value for the target pixel in the target block using at least one of: 1) pixels in adjacent blocks located in both directions of bidirectional intra prediction, 2) based on A weight for the distance between each pixel in the neighboring block and the target pixel, and 3) a weight for both directions.

The predicted value of the target pixel in the target block may be the value of the pixel in the predicted block.

The processing unit may use the derived prediction values to perform encoding and/or decoding in intra prediction.

At step 1810, the processing unit may, based on coding parameters related to the target block, information of the target picture, information of the target slice, quantization parameters, coding block flag (CBF), size of the target block, form of the target block, applied to the target The bidirectional intra prediction mode is derived by at least one of an entropy coding method of the block, an intra prediction mode of neighboring blocks of the target block, and a temporal layer level of the target block.

Optionally, in step 1820, the processing unit may be based on coding parameters related to the target block, information of the target picture, information of the target slice, quantization parameters, coding block flags (CBF), the size of the target block, the form of the target block , applied to at least one of an entropy coding method of the target block, an intra prediction mode of neighboring blocks of the target block, and a temporal layer level of the target block to derive a predicted value of a target pixel in the target block.

Determination of Bidirectional Intra Prediction Mode

Hereinafter, the bidirectional intra prediction mode may indicate the direction of bidirectional intra prediction. The terms "bidirectional intra prediction mode" and "direction of bidirectional intra prediction" may be used to have the same meaning and may be used interchangeably with each other.

19 shows a unidirectional intra prediction mode according to an example.

FIG. 20 shows a bidirectional intra prediction mode according to an example.

21 illustrates a bidirectional intra prediction mode using virtual neighboring pixels, according to an example.

The processing unit may determine and derive a bidirectional intra prediction mode based on at least one of: 1) an intra prediction mode indicator, 2) a unidirectional/bidirectional classification indicator, 3) MPM, 4) in a specified direction of the target block Availability of pixels in neighboring blocks above, and 5) prediction mode of neighboring blocks.

As shown in FIG. 19 , the unidirectional intra prediction mode may be an intra prediction mode that refers to pixels located in a single specified direction.

As shown in FIG. 20 , the bidirectional intra prediction mode may be an intra prediction mode that refers to pixels located in two specified directions.

Here, the pixel to be referenced may be a pixel adjacent to the target block. Pixels to be referenced for intra prediction may also be referred to as "samples".

Here, the term "pixels located in two specified directions" may mean "pixels located in a first specified direction and pixels located in a second specified direction".

As shown in FIG. 21, in the bidirectional intra prediction mode, pixels in the reconstructed adjacent blocks may be used to generate at least one virtual adjacent pixel located to the right of or below the target block. In other words, at least one virtual neighboring pixel may be located to the right of the target block or below the target block. The bidirectional intra-prediction mode may be an intra-prediction mode using pixels in the reconstructed neighboring blocks and virtual neighboring pixels with reference to pixels located in two specified directions.

Here, virtual neighboring pixels located to the right of the target block may be adjacent to and to the right of the target block. Here, virtual neighboring pixels located below the target block may be adjacent to and below the target block.

The processing unit may determine whether the bidirectional intra prediction mode is to be used for the target block based on at least one of the unidirectional/bidirectional classification indicator and the intra prediction mode indicator, and may derive the bidirectional intra prediction mode.

The unidirectional/bidirectional classification indicator may indicate whether bidirectional intra prediction mode is to be used for the target block. The one-way/two-way classification indicator can have any one of the first value and the second value. The first value may indicate that uni-directional intra prediction is used. For example, the first value may be "0". The second value may indicate that bidirectional intra prediction is used. For example, the second value may be "1".

The unidirectional/bidirectional classification indicator can be encoded and/or decoded in specific units (such as video, sequence, picture, slice, parallel block, CTU, CU, target block, sub-blocks of target block, and blocks with specific dimensions) The level of is signaled. In other words, a particular unit of encoding and/or decoding may include a unidirectional/bidirectional classification indicator that indicates whether bidirectional intra prediction mode is to be used for the target in the unit.

The bidirectional intra prediction mode may indicate two directions for bidirectional intra prediction. The two directions can be indicated using the schemes given in 1) to 4) below.

1) The number of intra prediction mode indicators may be two, and two directions of bidirectional intra prediction may be indicated by two intra prediction mode indicators, respectively.

Each of the two intra prediction mode indicators may indicate the direction of the unidirectional intra prediction mode. The two directions of bidirectional intra prediction may be determined by the two directions indicated by the two intra prediction mode indicators.

In this case, one intra-prediction mode indicator may indicate one direction for the intra-prediction mode, rather than distinguishing between the uni-directional prediction mode and the bi-directional prediction mode. Here, the direction may correspond to an angle such as 45°, 80° or 135°.

2) One intra prediction mode indicator may indicate any one of the direction of unidirectional intra prediction and the direction of bidirectional intra prediction.

For example, a value of "3" for the intra-prediction mode indicator may indicate 45° uni-directional intra-prediction, and a value of "70" for the intra-prediction mode indicator may indicate 45° and 225° bi-directional intra-prediction.

3) To indicate the direction of intra prediction, a unidirectional/bidirectional classification indicator and an intra prediction mode indicator may be used together.

The unidirectional/bidirectional classification indicator may indicate which of unidirectional intra prediction and bidirectional intra prediction is to be used, and the intra prediction mode indicator may indicate the direction of prediction.

For example, when the value of the unidirectional/bidirectional classification indicator is the second value and the value of the intra prediction mode indicator is 7, bidirectional intra prediction of 45° and 225° may be used, where 225° is the same as 45° Opposite Direction.

For example, when the value of the unidirectional/bidirectional classification indicator is the first value and the value of the intra prediction mode indicator is 7, 45° unidirectional intra prediction may be used.

4) When one intra-prediction mode indicator indicates a specified direction of uni-directional intra-prediction, bi-directional intra-prediction can be performed.

For example, when the intra prediction mode indicator indicates unidirectional prediction of 45°, bidirectional intra prediction of 45° and 225° may be performed, where 225° is the opposite direction to 45°.

22 illustrates the derivation and selection of bidirectional intra prediction from the direction of an intra prediction mode indicator, according to an example.

The processing unit may adaptively determine and derive the bidirectional intra-prediction mode based on 1) the intra-prediction mode indicator and 2) the availability of pixels in neighboring blocks of the target block.

As shown in FIG. 22, the intra prediction mode indicator may indicate one direction of the intra prediction mode, and additional directions corresponding to the direction of the intra prediction mode may be determined. Here, the additional direction may be a direction for bidirectional intra prediction determined according to the direction of the intra prediction mode.

The additional direction may be the opposite direction to that of the intra prediction.

Either one of uni-directional intra-prediction and bi-directional intra-prediction may be selected and derived according to the availability of reference pixels in the direction corresponding to the direction indicated by the intra-prediction mode indicator.

For example, either one of uni-directional intra-prediction and bi-directional intra-prediction may be selected and derived according to the availability of reference pixels in a direction opposite to that indicated by the intra-prediction mode indicator.

Here, when the reference pixels in the corresponding direction are available, bidirectional intra prediction can be selected, and when the reference pixels in the corresponding direction are not available, unidirectional intra prediction can be selected.

Hereinafter, the term "a (reference) pixel in a specified direction" may mean "a (reference) pixel located in a specified direction".

Here, the fact that the reference pixel is available may indicate that the value of the reference pixel has been determined. Alternatively, the fact that the reference pixels are available may indicate that the reconstruction of the reference pixels has been performed before performing intra prediction of the target block. The fact that the reference pixel is unavailable may indicate that the value of the reference pixel has not been determined. Alternatively, the fact that the reference pixel is unavailable may indicate that the reconstruction of the reference pixel has not been performed before performing intra prediction of the target block, and thus the value of the reference pixel has not been determined.

For example, when the intra-prediction mode indicator indicates an upper-right direction (eg, a 45° angle) and is available as a pixel in a neighboring block in a lower-left direction (eg, a 225° angle) in the opposite direction to the upper-right direction, the processing unit may It is determined that the intra prediction to be used for the target block is bidirectional intra prediction in two directions (ie, the upper right direction and the lower left direction).

For example, when the intra prediction mode indicator indicates an upper-right direction (eg, a 45° angle) and pixels in a neighboring block in a lower-left direction (eg, a direction at a 225-degree angle), which is the opposite direction to the upper-right direction, are unavailable, processing The unit may determine that the intra prediction to be used for the target block is unidirectional intra prediction in the upper-right direction.

A unit for determination and derivation of the intra prediction mode may be a target block. The selection of the intra prediction mode may be to determine which of unidirectional intra prediction and bidirectional intra prediction will be used. That is, it can be adaptively determined which of unidirectional intra prediction and bidirectional intra prediction is to be used for the entire target block.

Hereinafter, the intra prediction direction indicated by the intra prediction mode indicator may be designated as a 'first direction', and the second direction may designate a direction corresponding to the first direction or a direction opposite to the first direction.

For example, bidirectional intra prediction in the first and second directions may be used when all reference pixels in the first direction and all reference pixels in the second direction are available for all pixels in the target block. For all pixels in the target block, when there is at least one unavailable reference pixel among all reference pixels in the second direction, unidirectional intra prediction in the first direction may be used.

The unit for determination and derivation of the intra prediction mode may be each pixel in the target block. That is, it can be adaptively determined which of unidirectional intra prediction and bidirectional intra prediction is to be used for each of the pixels in the target block.

For example, for a particular pixel in the target block, when reference pixels in the first direction and reference pixels in the second direction are available, bidirectional intra prediction in the first and second directions may be used. For a specific pixel in the target block, when reference pixels in the second direction are not available, unidirectional intra prediction in the first direction may be used.

When reference pixels in the first direction or reference pixels in the second direction are unavailable, the processing unit may use padding to generate values for the unavailable reference pixels. Here, the value to be used for the padding of the unavailable reference pixel may be the value of the available reference pixel closest to the unavailable reference pixel. When there are multiple reference pixels closest to the unavailable reference pixel, the value used to fill the unavailable reference pixel may be an average of the values of the multiple closest available reference pixels.

With padding, unavailable reference pixels can be made available, and unidirectional intra prediction or bidirectional intra prediction using the available reference pixels can be performed.

The second direction may be a collinear direction opposite to the first direction indicated by the intra prediction mode indicator. In other words, the second direction may be a direction created by adding 180° to the first direction. Alternatively, the second direction may be a direction adding a predefined angle (α) to the first direction indicated by the intra prediction mode indicator. The predefined angle (α) may be set to the same value in the encoding apparatus 1600 and the decoding apparatus 1700 , and may be signaled from the encoding apparatus 1600 to the decoding apparatus 1700 .

As described above, the intra prediction mode indicator in an embodiment may not distinguish unidirectional mode from bidirectional mode, and may indicate the direction of intra prediction.

The processing unit may select a bidirectional intra prediction mode for the target block based on at least one of: 1) MPM, 2) unidirectional/bidirectional classification indicator, 3) intra prediction mode of neighboring blocks, and 4) specified Availability of reference pixels in the orientation.

The processing unit may use the intra-prediction modes of neighboring blocks and the MPM to determine a bidirectional intra-prediction mode for the target block.

The processing unit may use intra-prediction modes of neighboring blocks of the target block and the MPM to determine a bidirectional intra-prediction mode for the target block.

For example, when bidirectional intra prediction has been used for at least one of the adjacent blocks and at least one of the MPMs of the target block matches the bidirectional intra prediction mode of the adjacent block, the processing unit may use the bidirectional intra prediction of the matched MPM The prediction mode is determined as a bidirectional intra prediction mode of the target block.

For example, the processing unit may determine a bidirectional intra-prediction mode for the target block using MPMs in both directions of the N MPMs for the target block. N may be an integer of 2 or greater. For example, N can be 6.

The processing unit may determine a bidirectional intra prediction mode for the target block using intra prediction modes, MPM, and unidirectional/bidirectional classification indicators of neighboring blocks of the target block.

For example, when the unidirectional/bidirectional classification indicator indicates that bidirectional intra prediction is used, the processing unit may use one of the MPMs of the target block to determine the bidirectional intra prediction mode for the target block. For example, the MPM to be used may be the first MPM in the MPM list.

The processing unit may select a bidirectional intra-prediction mode for the target block based on the intra-prediction mode of the neighboring block, the MPM, and the availability of reference pixels in a direction opposite the intra-prediction direction of the neighboring block.

For example, the processing unit may be configured to derive the direction of intra prediction for the target block from any of the MPMs of the target block, and may be configured to, when a reference pixel in a direction corresponding to the derived direction is available, convert the The derived direction and the bidirectional intra prediction mode in the corresponding direction are used for intra prediction of the target block.

Intra prediction using bidirectional intra prediction mode

When the intra prediction mode of the target block is derived and selected as the bidirectional intra prediction mode, the processing unit may determine by referring to at least one of pixels located in adjacent blocks in both prediction directions of the bidirectional intra prediction mode The predicted value for the target pixel.

Here, the target pixel may be a pixel targeted for prediction, and may be a pixel in a target block or a pixel in a prediction block for the target block. In other words, the prediction value for the target block may be determined through bidirectional intra prediction according to the bidirectional intra prediction mode.

In such bidirectional intra prediction, the processing unit may obtain reference pixels in each prediction direction by filtering pixels located in adjacent blocks in each prediction direction of the bidirectional intra prediction. The processing unit may use at least one of the obtained reference pixels to derive a predicted value for the target pixel.

In other words, the reference pixel may be a pixel in an adjacent block, and may be a pixel at a position specified by the specified prediction direction of the pixel in the target block. Alternatively, the reference pixel may be a value obtained by applying filtering to pixels adjacent to the position specified by the specified prediction direction of the pixels in the target block.

The processing unit may determine the predicted value for the target pixel using at least one of the reference pixels in the two prediction directions of the bidirectional intra prediction mode.

When at least one of the reference pixels in the two prediction directions of the bidirectional intra prediction mode is used, weights may be applied to the respective reference pixels. Weights can be predefined. Optionally, the weights can be set by calculation.

For example, the weights may be set based on the distance between the target pixel and each reference pixel. The weight may be inversely proportional to the distance between the target pixel and each reference pixel. Alternatively, the weight may be proportional to the distance between the target pixel and each reference pixel. The ratio of the weights of the reference pixels may be the inverse of the ratio of the distances between the respective reference pixels and the target pixel.

The weights of reference pixels may differ according to the prediction direction.

The weight of each reference pixel may differ according to whether the corresponding reference pixel is a reference pixel in the direction indicated by the intra prediction mode indicator. For example, the weight of the direction indicated by the intra prediction mode indicator may be α, and the weight of the direction corresponding to the indicated direction may be 1-α. α can be a real number greater than 0 and less than 1. For example, a can be 2/3.

Alternatively, the weight of each reference pixel may be set based on the distance between the target pixel and the corresponding reference pixel and based on whether the reference pixel is a reference pixel in the direction indicated by the intra prediction mode indicator.

The weights may be set by the encoding apparatus 1600, and the set weights may be signaled from the encoding apparatus 1600 to the decoding apparatus 1700 through a bitstream.

When the weight of one of the two prediction directions of the bidirectional intra prediction mode is signaled, the weight of the other prediction direction may be set based on the signaled weight.

Each may be signaled at the level of a specific unit of encoding and/or decoding, such as a video, sequence, picture, slice, parallel block, CTU, CU, target block, sub-blocks of a target block, and blocks of a specific size. Weights. In other words, a particular unit of encoding and/or decoding may include weights to be used for objects in the corresponding unit or information to be used to derive the weights.

Bidirectional intra prediction using virtual pixels

23 illustrates the generation of virtual neighboring pixels according to an example.

Since some of the pixels in the two prediction directions of the bidirectional intra prediction mode are not reconstructed before the bidirectional intra prediction, they may not be used for the bidirectional intra prediction. The processing unit may generate virtual neighboring pixels corresponding to the pixels that have not been reconstructed, and may use the virtual neighboring pixels to perform bidirectional intra prediction.

The neighboring pixels may be reconstructed pixels in a reconstructed neighboring block. Each virtual neighboring pixel may be a pixel generated using one or more reconstructed pixels. In other words, the values of virtual neighboring pixels may be generated based on the values of one or more reconstructed pixels.

For example, a virtual neighboring pixel may be a pixel adjacent to and above or to the left of the target block. Virtual neighboring pixels may be pixels adjacent to and below or to the right of the target block.

A virtual neighboring pixel for the target block may be a pixel in a virtual neighboring block for the target block. A virtual neighbor block may be an unreconstructed block adjacent to the target block. For example, a virtual neighboring block may be a block adjacent to and below or to the right of the target block.

When the intra prediction mode of the target block is derived and determined to be the bidirectional intra prediction mode, the processing unit may refer to at least one of adjacent pixels and virtual adjacent pixels located in the two prediction directions of the bidirectional intra prediction mode Determine the predicted value for the target pixel.

When performing prediction in this manner, the processing unit may obtain reference pixels in each prediction direction by filtering neighboring pixels in each prediction direction. In addition, the processing unit obtains reference pixels in each prediction direction by filtering virtual neighboring pixels in each prediction direction. The processing unit may use at least one of the obtained reference pixels to derive a predicted value for the target pixel.

In other words, the reference pixel may be an adjacent pixel or a virtual adjacent pixel, and may be a pixel at a position specified by a specified prediction direction of a pixel in the target block. Alternatively, the reference pixel may be a value obtained by applying filtering to neighboring pixels and/or virtual neighboring pixels adjacent to the position specified by the specified prediction direction of the pixel in the target block.

The processing unit may determine the predicted value for the target pixel using at least one of the reference pixels in the two prediction directions of the bidirectional intra prediction mode. Reference pixels may include adjacent pixels and virtual adjacent pixels.

The foregoing description of weights may also be applied to virtual neighboring pixels. When at least one of the reference pixels in the two prediction directions of the bidirectional intra prediction mode is used, weights may be applied to neighboring pixels and virtual neighboring pixels that are reference pixels, respectively.

Below, an exemplary method for generating virtual neighboring pixels will be described.

The upper left coordinate of the target block may be (Cx,Cy). W can be the horizontal size of the target block. H can be the height or vertical dimension of the target block.

Hereinafter, "pixel (α, β)" may refer to a pixel having coordinates (α, β).

1) The processing unit may generate virtual neighboring pixels based on pixels in the reconstructed neighboring blocks.

The virtual neighbor pixels may include a right virtual neighbor pixel adjacent to and to the right of the target block and a lower virtual neighbor pixel adjacent to and below the target block.

The position of the right virtual neighbor pixel can be given by Equation 2 below:

[Equation 2]

N(Cx+W,y), where (y∈{Cy,Cy+1,Cy+2,…,Cy+H})

The position of the lower virtual neighbor pixel can be given by Equation 3 below:

[Equation 3]

N(x,Cy+H), where (x∈{Cx,Cx+1,Cx+2,…,Cx+W})

2) The processing unit may generate virtual neighboring pixels (Cx+W, Cy) based on one or more of the reconstructed neighboring pixels adjacent to and above the target block.

For example, in FIG. 23 , virtual neighboring pixels R may be generated using one or more of the reconstructed neighboring pixels adjacent to and above the target block. The virtual neighboring pixel R may be the uppermost virtual neighboring pixel among the right virtual neighboring pixels.

3) The processing unit may generate a virtual adjacent pixel (Cx+W, Cy) based on the adjacent pixel (Cx+W, Cy-1).

For example, in FIG. 23, a virtual neighboring pixel R may be generated based on the neighboring pixel b. The virtual neighboring pixel R may be the uppermost virtual neighboring pixel among the right virtual neighboring pixels. The adjacent pixel b may be a pixel adjacent to and above the virtual adjacent pixel R.

For example, the relationship between the virtual neighboring pixel R and the neighboring pixel b can be represented by the following Equation 4:

[Equation 4]

R=b

4) The processing unit may be based on one or more of neighboring pixels (Cx+W-1, Cy-1), neighboring pixels (Cx+W, Cy-1), and neighboring pixels (Cx+W+1, Cy-1). multiple to generate virtual adjacent pixels (Cx+W,Cy).

For example, in FIG. 23, the virtual neighboring pixel R may be generated using the neighboring pixel a, the neighboring pixel b, and the neighboring pixel c. The virtual neighboring pixel R may be the uppermost virtual neighboring pixel among the right virtual neighboring pixels.

The coordinates of neighboring pixel a, neighboring pixel b, and neighboring pixel c are given by Equation 5, Equation 6, and Equation 7 below:

[Equation 5]

(Cx+W-1,Cy-1)

[Equation 6]

(Cx+W,Cy-1)

[Equation 7]

(Cx+W+1,Cy-1)

In other words, the adjacent pixel b may be a pixel adjacent to and above the virtual adjacent pixel R. The adjacent pixel a may be a pixel adjacent to the adjacent pixel b and to the left of the adjacent pixel b. The adjacent pixel c may be a pixel adjacent to and to the right of the adjacent pixel b.

For example, in FIG. 23, the virtual neighboring pixel R may be a weighted sum of the neighboring pixel a, the neighboring pixel b, and the neighboring pixel c. When the virtual neighboring pixel R is generated, weights may be assigned to the neighboring pixel a, the neighboring pixel b, and the neighboring pixel c, respectively.

For example, the relationship between the virtual neighboring pixel R, the neighboring pixel a, the neighboring pixel b, and the neighboring pixel c can be represented by the following Equation 8:

[Equation 8]

R=1/4*a+2/4*b+1/4*c=1/4*a+1/2*b+1/4*c=(a+b<<1+c)>> 2

Here, "<<" can be a left shift operator. ">>" can be a right shift operator.

5) Similar to requirements 2) to 4) above, the processing unit may generate virtual adjacent pixels (Cx, Cy+H) based on one or more of the reconstructed adjacent pixels adjacent to and to the left of the target block .

For example, in FIG. 23, a virtual neighboring pixel L may be generated using one or more of the reconstructed neighboring pixels adjacent to and to the left of the target block. The virtual neighboring pixel L may be the leftmost virtual neighboring pixel among the lower virtual neighboring pixels.

6) The processing unit may generate virtual neighboring pixels (Cx, Cy+H) based on neighboring pixels (Cx-1, Cy+H).

For example, in FIG. 23, a virtual neighboring pixel L may be generated using the neighboring pixel q. The virtual neighboring pixel L may be the leftmost virtual neighboring pixel among the lower virtual neighboring pixels. The adjacent pixel q may be a pixel adjacent to and to the left of the virtual adjacent pixel L.

For example, the relationship between the virtual neighboring pixel L and the neighboring pixel q can be represented by the following Equation 9:

[Equation 9]

L=q

7) The processing unit may be based on one or more of neighboring pixels (Cx-1, Cy+H-1), neighboring pixels (Cx-1, Cy+H), and neighboring pixels (Cx-1, Cy+H+1). multiple to generate virtual adjacent pixels (Cx, Cy+H).

For example, in FIG. 23, a virtual neighboring pixel L may be generated using the neighboring pixel p, the neighboring pixel q, and the neighboring pixel r. The virtual neighboring pixel L may be the leftmost virtual neighboring pixel among the lower virtual neighboring pixels.

The coordinates of the neighboring pixel p, the neighboring pixel q, and the neighboring pixel r can be given by Equation 10, Equation 11, and Equation 12 below.

[Equation 10]

(Cx-1,Cy+H-1)

[Equation 11]

(Cx-1,Cy+H)

[Equation 12]

(Cx-1,Cy+H+1)

In other words, the adjacent pixel q may be a pixel adjacent to and to the left of the virtual adjacent pixel L. The adjacent pixel p may be a pixel adjacent to and above the adjacent pixel q. The adjacent pixel r may be a pixel adjacent to and below the adjacent pixel q.

For example, in FIG. 23, the virtual neighboring pixel L may be a weighted sum of the neighboring pixel p, the neighboring pixel q, and the neighboring pixel r. When the virtual neighboring pixel L is generated, respective weights may be assigned to the neighboring pixel p, the neighboring pixel q, and the neighboring pixel r.

For example, the relationship between the virtual neighboring pixel L, the neighboring pixel p, the neighboring pixel q, and the neighboring pixel r can be represented by the following Equation 13:

[Equation 13]

L=1/4*p+2/4*q+1/4*r=1/4*p+1/2*q+1/4*r=(p+q<<1+r)>> 2

8) The processing unit may generate additional virtual neighboring pixels based on the plurality of virtual neighboring pixels generated using neighboring pixels.

For example, in FIG. 23 , the virtual neighboring pixel N _i may be generated based on the virtual neighboring pixel R and the virtual neighboring pixel L. The virtual neighboring pixel N _i may be a virtual neighboring pixel between the virtual neighboring pixel R and the virtual neighboring pixel L.

24 illustrates the use of virtual neighboring pixels to generate additional virtual neighboring pixels, according to an example.

As shown in FIG. 24 , the virtual neighboring pixels for the target block may be arranged in a row according to the distance from the virtual neighboring pixel L and the distance from the virtual neighboring pixel R.

The distance between a specific virtual neighboring pixel N _i and a virtual neighboring pixel L can be represented by the following Equation 14:

[Equation 14]

(absolute value of the difference between the x-coordinate of _Ni and the x-coordinate of L)+(absolute value of the difference between the y-coordinate of _Ni and the y-coordinate of L)

The distance between a specific virtual neighboring pixel N _i and a virtual neighboring pixel R can be represented by the following equation 15:

[Equation 15]

(absolute value of the difference between the x-coordinate of _Ni and the x-coordinate of R)+(absolute value of the difference between the y-coordinate of _Ni and the y-coordinate of R)

In other words, the distance between pixels may be the sum of the absolute value of the difference between the x-coordinates of the pixels and the absolute value of the difference between the y-coordinates of the pixels.

9) The processing unit may generate a virtual neighboring pixel L and a virtual neighboring pixel R based on neighboring pixels in the reconstructed neighboring block, and may generate a virtual neighboring pixel L and a virtual neighboring pixel R based on the virtual neighboring pixel L and the virtual neighboring pixel R. of virtual neighboring pixels N _i .

A weight for distance may be used when generating virtual neighboring pixels _Ni . The weight for the distance may include a weight according to the distance between the virtual neighboring pixel N _i and the virtual neighboring pixel L and a weight according to the distance between the virtual neighboring pixel N _i and the virtual neighboring pixel R.

For example, the relationship between virtual neighbor N _i , virtual neighbor L, and virtual neighbor R can be represented by Equation 16 below:

[Equation 16]

d _R may be the distance between the virtual neighboring pixel N _i and the virtual neighboring pixel R .

d _L may be the distance between the virtual neighbor pixel N _i and the virtual neighbor pixel L .

FIG. 25 illustrates the generation of lower right virtual neighbor pixels and middle virtual neighbor pixels, according to an example.

The upper left coordinate of the target block may be (Cx,Cy). W can be the horizontal size of the target block. H can be the height or vertical dimension of the target block.

10) The processing unit may generate virtual neighboring pixels (Cx) based on one or more of reconstructed neighboring pixels adjacent to and above the target block and reconstructed neighboring pixels adjacent to and to the left of the target block. +W,Cy+H).

For example, in FIG. 25, virtual neighbors may be generated using one or more of reconstructed neighbor pixels adjacent to and above the target block and reconstructed neighbor pixels adjacent to and to the left of the target block pixel G. The virtual neighboring pixel G may be the lower right virtual neighboring pixel. In other words, the virtual neighbor G may be a pixel adjacent to and to the right of the lower virtual neighbor, and may be a pixel adjacent to and below the right virtual neighbor.

11) The processing unit may generate a virtual adjacent pixel (Cx+W, Cy+H) based on the adjacent pixel (Cx+W, Cy-1) and the adjacent pixel (Cx-1, Cy+H).

For example, in FIG. 25, a virtual adjacent pixel G may be generated based on the adjacent pixel b and the adjacent pixel q. The virtual neighboring pixel G may be the lower right virtual neighboring pixel. The adjacent pixel b may be a pixel adjacent to the upper right portion of the target block. The adjacent pixel q may be a pixel adjacent to the lower left portion of the target block.

For example, the relationship between the virtual neighboring pixel G, the neighboring pixel b, and the neighboring pixel q can be represented by the following Equation 17:

[Equation 17]

G=1/2*(b+q)=(b+q)>>1

12) The processing unit may generate a virtual neighbor pixel (Cx+W, Cy+H) based on the virtual neighbor pixel (Cx+W, Cy) and the virtual neighbor pixel (Cx, Cy+H).

For example, in FIG. 25, a virtual neighboring pixel R and a virtual neighboring pixel L may be used to generate a virtual neighboring pixel G. The virtual neighboring pixel G may be the lower right virtual neighboring pixel. The virtual neighboring pixel R may be the uppermost virtual neighboring pixel among the right virtual neighboring pixels. The virtual neighboring pixel L may be the leftmost virtual neighboring pixel among the lower virtual neighboring pixels.

For example, the relationship between virtual neighbor G, virtual neighbor R, and virtual neighbor L can be represented by the following Equation 18:

[Equation 18]

G=1/2*(R+L)=(R+L)>>1

12) The processing unit may generate a third virtual neighboring pixel based on the first virtual neighboring pixel and the second virtual neighboring pixel, and may generate a fourth virtual neighboring pixel based on the first virtual neighboring pixel and the third virtual neighboring pixel.

The processing unit may generate a virtual neighbor (Cx+W,Cy) based on the virtual neighbor (Cx+W,Cy), the virtual neighbor (Cx,Cy+H), and the virtual neighbor (Cx+W,Cy+H) The virtual neighbors between the virtual neighbors (Cx+W, Cy+H). Additionally, the processing unit may generate a virtual neighbor (Cx,Cy+) from the virtual neighbor (Cx+W,Cy), the virtual neighbor (Cx,Cy+H), and the virtual neighbor (Cx+W,Cy+H) H) and virtual neighbors (Cx+W, Cy+H) between virtual neighbors.

For example, in FIG. 25 , virtual neighboring pixels M _i may be generated based on virtual neighboring pixels R, virtual neighboring pixels L, and virtual neighboring pixels G. The virtual neighboring pixel M _i may be a pixel between the virtual neighboring pixel R and the virtual neighboring pixel G.

For example, in FIG. 25 , virtual neighboring pixels R, virtual neighboring pixels L, and virtual neighboring pixels G may be used to generate virtual neighboring pixels N _i . The virtual neighboring pixel N _i may be a pixel between the virtual neighboring pixel L and the virtual neighboring pixel G.

13) The processing unit may generate a third virtual neighboring pixel based on the first virtual neighboring pixel and the second virtual neighboring pixel, and may generate a fourth virtual neighboring pixel based on the first virtual neighboring pixel and the third virtual neighboring pixel. Here, when generating the fourth virtual neighboring pixel, the processing unit may use the weight for the additional virtual neighboring pixel. The additional virtual neighboring pixels may include a first virtual neighboring pixel and a third virtual neighboring pixel. The weight for the additional virtual neighboring pixel may be set based on the distance between the fourth virtual neighboring pixel and the additional virtual neighboring pixel.

For example, in FIG. 25 , virtual neighboring pixels M _i may be generated based on virtual neighboring pixels R, virtual neighboring pixels L, and virtual neighboring pixels G. The virtual neighboring pixel M _i may be a pixel between the virtual neighboring pixel R and the virtual neighboring pixel G.

When generating the virtual neighboring pixel _Mi , one or more of the weight for the virtual neighboring pixel R, the weight for the virtual neighboring pixel L, and the weight for the virtual neighboring pixel G may be used.

The weight for the virtual neighboring pixel R may be set based on the distance between the virtual neighboring pixel R and the virtual neighboring pixel _Mi.

The weight for the virtual neighboring pixel L may be set based on the distance between the virtual neighboring pixel L and the virtual neighboring pixel _Mi.

The weight for the virtual neighboring pixel G may be set based on the distance between the virtual neighboring pixel G and the virtual neighboring pixel _Mi.

For example, in FIG. 25 , virtual neighboring pixels R, virtual neighboring pixels L, and virtual neighboring pixels G may be used to generate virtual neighboring pixels N _i . The virtual neighboring pixel N _i may be a pixel between the virtual neighboring pixel L and the virtual neighboring pixel G.

When generating the virtual neighbor pixel _Ni , one or more of the weight for the virtual neighbor pixel R, the weight for the virtual neighbor pixel L, and the weight for the virtual neighbor pixel G may be used.

The weight for the virtual neighboring pixel R may be set based on the distance between the virtual neighboring pixel R and the virtual neighboring pixel _Ni .

The weight for the virtual neighboring pixel L may be set based on the distance between the virtual neighboring pixel L and the virtual neighboring pixel _Ni .

The weight for the virtual neighboring pixel G may be set based on the _distance between the virtual neighboring pixel G and the virtual neighboring pixel Ni.

The weight for the virtual neighboring pixel L may be set based on the _distance between the virtual neighboring pixel G and the virtual neighboring pixel Ni. The weight for the virtual neighbor L may be proportional to the distance between the virtual neighbor G and the virtual neighbor _Ni . The weight for the virtual neighboring pixel L may be inversely proportional to the sum of the distance from the virtual neighboring pixel _Ni to the virtual neighboring pixel L and the distance from the virtual neighboring pixel _Ni to the virtual neighboring pixel G.

The weight for the virtual neighboring pixel G may be set based on the distance between the virtual neighboring pixel L and the virtual neighboring pixel _Ni . The weight for the virtual neighbor G may be proportional to the distance between the virtual neighbor L and the virtual neighbor _Ni . The weight for the virtual neighboring pixel G may be inversely proportional to the sum of the distance from the virtual neighboring pixel _Ni to the virtual neighboring pixel L and the distance from the virtual neighboring pixel _Ni to the virtual neighboring pixel G.

For example, the relationship between virtual neighbor N _i , virtual neighbor L, and virtual neighbor G can be represented by the following Equation 19:

[Equation 19]

d _G may be the distance between the virtual neighbor pixel N _i and the virtual neighbor pixel G .

d _L may be the distance between the virtual neighbor pixel N _i and the virtual neighbor pixel L .

For example, the relationship among the virtual neighboring pixels M _i , the virtual neighboring pixels R, and the virtual neighboring pixels G can be represented by Equation 20 below.

[Equation 20]

d _G may be the distance between the virtual neighboring pixel _Mi and the virtual neighboring pixel G.

d _R may be the distance between the virtual neighboring pixel _Mi and the virtual neighboring pixel R.

FIG. 26 shows bidirectional intra prediction according to an example.

The processing unit may derive a prediction value for the target pixel using at least one of reconstructed neighbor pixels and virtual neighbor pixels in both prediction directions of the bidirectional intra prediction mode.

The processing unit may derive a prediction value for the target pixel X using one or more of the two reference pixels located in the two prediction directions of the bidirectional intra prediction mode.

The two reference pixels may include reference pixel Ref_A and reference pixel Ref_B.

Ref_A and Ref_B may be pixels located in two prediction directions respectively derived and selected via bidirectional intra prediction of the target pixel.

The two reference pixels may be reconstructed adjacent pixels. For example, as shown in FIG. 26, both Ref_A and Ref_B may be adjacent pixels.

27 illustrates bidirectional intra prediction using virtual neighboring pixels, according to an example.

The processing unit may derive a prediction value for the target pixel X using one or more of the two reference pixels located in the two prediction directions of the bidirectional intra prediction mode.

The two reference pixels may include reference pixel Ref_A and reference pixel Ref_B.

Ref_A and Ref_B may be pixels located in two prediction directions respectively derived and selected via bidirectional intra prediction of the target pixel.

At least one of the two reference pixels may be a virtual adjacent pixel. For example, as shown in FIG. 27, Ref_A may be a neighboring pixel, and Ref_B may be a virtual neighboring pixel.

Such a reference pixel may be a pixel at a specific position in each of the two prediction directions of bidirectional intra prediction. The processing unit may obtain reference pixels by performing filtering on one or more of neighboring pixels and/or virtual neighboring pixels near a particular location.

For example, when the particular location is not indicated by integer coordinates, the processing unit may obtain reference pixels by performing filtering on one or more of neighboring pixels and/or virtual neighboring pixels near the particular location.

For example, when a pixel at a particular location is unavailable, the processing unit may obtain a reference pixel by performing filtering on one or more of neighboring pixels and/or virtual neighboring pixels near the particular location.

Neighboring pixels near the specific location may be neighboring pixels adjacent to the specific location. The virtual neighboring pixels near the specific location may be virtual neighboring pixels adjacent to the specific location.

The predicted value Pred_X derived for the target pixel may be a statistical value associated with one or more of Ref_A and Ref_B, and the predicted value Pred_X may be derived based on the statistical value. Hereinafter, the statistical value in the embodiment may be at least one of an average value, a weighted average value, a maximum value, a minimum value, a mode, a median value, and an interpolated value.

As illustrated in Equation 21 below, Ref_A and Ref_b may be used to derive the predicted value Pred_X for the target pixel.

[Equation 21]

Pred_X=F(Ref_A,Ref_B)

F() can be a specific function.

As described above, the processing unit may derive a prediction value for the target pixel X using one or more of the two reference pixels located in the two prediction directions of the bidirectional intra prediction mode. Here, when deriving the prediction value for the target pixel X, the processing unit may apply weights to the two reference pixels located in the two prediction directions, respectively.

For example, the sum of the weights can be 1.

The two reference pixels may include reference pixel Ref_A and reference pixel Ref_B.

Ref_A and Ref_B may be pixels located in two prediction directions respectively derived and selected via bidirectional intra prediction of the target pixel.

For example, as shown in FIG. 26, both Ref_A and Ref_B may be reconstructed neighboring pixels.

Alternatively, in an example, as shown in FIG. 27, Ref_A may be a reconstructed neighboring pixel, and Ref_B may be a virtual neighboring pixel.

As illustrated in Equation 22 below, the predicted value Pred_X for the target pixel may be derived using the weights for Ref_A and the weights for Ref_B.

[Equation 22]

Pred_X=Dir_A*Ref_A+Dir_B*Ref_B

Dir_A may be a weight for Ref_A. Dir_B may be a weight for Ref_B.

The sum of Dir_A and Dir_B may be 1.

When generating the derived prediction value Pred_X for the target block, the processing unit may use the filtering described above to obtain reference pixels and weights for the reference pixels together.

Such a reference pixel may be a pixel at a specific position in each of the two prediction directions of bidirectional intra prediction. The processing unit may obtain reference pixels by performing filtering on one or more of neighboring pixels and/or virtual neighboring pixels near a particular location. Additionally, the processing unit may apply corresponding weights to the generated reference pixels.

28 illustrates bidirectional intra prediction using distances between neighboring pixels and target pixels, according to an example.

29 illustrates bidirectional intra prediction using distances between virtual neighboring pixels and target pixels, according to an example.

As described above, the processing unit may derive a prediction value for the target pixel X using one or more of the two reference pixels located in the two prediction directions of the bidirectional intra prediction mode. Here, the processing unit may use a weight according to the distance between the corresponding reference pixel and the target pixel for each of the two reference pixels located in the two prediction directions.

The two reference pixels may include reference pixel Ref_A and reference pixel Ref_B.

Ref_A and Ref_B may be pixels located in two prediction directions respectively derived and selected via bidirectional intra prediction of the target pixel.

For example, as shown in FIG. 28, both Ref_A and Ref_B may be reconstructed neighboring pixels.

Alternatively, in an example, as shown in FIG. 29, Ref_A may be a reconstructed neighboring pixel, and Ref_B may be a virtual neighboring pixel.

When generating the derived prediction value Pred_X for the target block, the processing unit may use the filtering described above to obtain the reference pixels together with the weights according to the distance between the reference pixels and the target pixels.

Such a reference pixel may be a pixel at a specific position in each of the two prediction directions of bidirectional intra prediction. The processing unit may obtain reference pixels by performing filtering on one or more of neighboring pixels and/or virtual neighboring pixels near a particular location. Additionally, the processing unit may apply corresponding weights to the generated reference pixels.

As illustrated in Equation 23 below, one or more of Ref_A, Dis_A, Ref_B, and Dis_B may be used to derive the predicted value Pred_X for the target pixel.

[Equation 23]

Pred_X＝F(Ref_A,Dis_A,Ref_B,Dis_B)

F() can be a specific function.

Dis_A can be the distance between the target pixel and Ref_A. Dis_B can be the distance between the target pixel and Ref_B.

The derived predicted value Pred_X for the target pixel may be a statistical value associated with one or more of Ref_A, Dis_A, Ref_B, and Dis_B, and the predicted value Pred_X may be derived based on the statistical value.

As illustrated in Equation 24 below, the predicted value Pred_X for the target pixel may be derived based on a weight according to the distance between the target pixel and the corresponding reference pixel.

[Equation 24]

The weight for one of the two reference pixels may be proportional to the distance between the other of the two reference pixels and the target pixel.

The weight for one of the two reference pixels may be inversely proportional to the sum of the distances from the target pixel to the two reference pixels.

For example, the weight for Ref_B can be given by Equation 25 below:

[Equation 25]

For example, the weight for Ref_A may be given by Equation 26 below.

[Equation 26]

As described above, the processing unit may derive a prediction value for the target pixel X using one or more of the two reference pixels located in the two prediction directions of the bidirectional intra prediction mode. Here, the processing unit may use one or more of a distance weight and a direction weight for each of the two reference pixels in the two prediction directions.

The distance weight may be a weight according to the distance between the corresponding reference pixel and the target pixel. The direction weight may be a weight according to the direction from the target pixel to the corresponding reference pixel.

When generating the derived prediction value Pred_X for the target block, the processing unit may use the filtering described above to obtain reference pixels, distance weights, and direction weights together.

Such a reference pixel may be a pixel at a specific position in each of the two prediction directions of bidirectional intra prediction. The processing unit may obtain reference pixels by performing filtering on one or more of neighboring pixels and/or virtual neighboring pixels near a particular location. Additionally, the processing unit may apply one or more of distance weights and direction weights to the generated reference pixels.

As illustrated in Equation 27 below, one or more of Ref_A, Dis_A, Dir_A, Ref_B, Dis_B, and Dir_B may be used to derive the predicted value Pred_X for the target pixel.

[Equation 27]

Pred_X＝F(Ref_A,Dis_A,Dir_A,Ref_B,Dis_B,Dir_B)

F() can be a specific function.

Dis_A can be the distance between the target pixel and Ref_A. Dir_A can be the direction of Ref_A. Dir_A can be the direction from the target pixel to Ref_A. Dis_B can be the distance between the target pixel and Ref_B. Dir_B can be the direction of Ref_B. Dir_B can be the direction from the target pixel to Ref_B.

The derived predicted value Pred_X for the target pixel may be a statistical value associated with one or more of Ref_A, Dis_A, Dir_A, Ref_B, Dis_B, and Dir_B, and the predicted value Pred_X may be derived based on the statistical value.

As illustrated in Equation 28 below, the predicted value Pred_X for the target pixel may be derived based on the distance from the target pixel to the reference pixel and the directional weight for the reference pixel.

[Equation 28]

The weight for one of the two reference pixels may be proportional to the distance between the other of the two reference pixels and the target pixel.

Furthermore, the weight for one of the two reference pixels may be proportional to the directional weight for the one reference pixel.

The weight for one of the two reference pixels may be inversely proportional to the sum of the distances from the target pixel to the two reference pixels.

For example, the weight for Ref_B can be given by Equation 29 below:

[Equation 29]

For example, the weight for Ref_A can be given by the following equation 30:

[Equation 30]

Use MPM to derive intra prediction mode

When the intra prediction mode of the target block is determined, the possibility that a specific intra prediction mode will be used for the intra prediction of the target block may be high or low according to encoding parameters related to the target block. Considering this possibility, MPM lists can be used.

The remaining modes may be remaining intra prediction modes other than the MPMs in the MPM list. In other words, the remaining modes may be remaining intra prediction modes after excluding one or more MPMs in the MPM list from all intra prediction modes.

According to the probability that the remaining modes will be used for intra prediction of the target block, the remaining modes may be classified into a first remaining mode set and a second remaining mode set.

A residual mode with a high probability of being used for intra prediction of the target block may be defined as a first residual mode set. The first set of remaining modes may be referred to as "possible remaining modes". In other words, the possible remaining mode may indicate an intra prediction mode of the remaining intra prediction modes (ie, of all intra prediction modes except MPM) that is used as the intra prediction mode of the target block with a high probability.

The remaining modes that are not included in the first remaining mode set among all remaining modes may be defined as the second remaining mode set. The second set of residual modes may be referred to as "pure (true) residual modes".

The remaining mode indicator may indicate a remaining mode to be used for intra prediction of the target block among the remaining modes. Optionally, the remaining mode indicator may indicate a remaining mode to be used for intra prediction of the target block among remaining modes as possible remaining modes.

FIG. 30 illustrates determination of intra prediction mode using residual mode, according to an embodiment.

At step 3010, the processing unit may derive one or more MPMs for the target block.

The processing unit may derive one or more MPMs in the list of MPMs for the target block.

In step 3020, the processing unit may determine whether the intra-prediction mode of the target block is one of the MPMs.

The processing unit may use the MPM usage indicator to determine whether the intra prediction mode of the target block is one of the MPMs. The processing unit may obtain the MPM usage indicator from the bitstream.

For example, the MPM usage indicator may have a name such as "prev_intra_pred_mode flag".

When the value of the MPM usage indicator is a first value (eg, "1"), the processing unit may determine that the intra prediction mode of the target block is one of the MPMs.

When the value of the MPM usage indicator is the second value (eg, "0"), the processing unit may determine that the intra prediction mode of the target block is not one of the MPMs.

If it is determined that the intra prediction mode of the target block is one of the MPMs, step 3030 may be performed.

If it is determined that the intra prediction mode of the target block is not one of the MPMs, step 3040 may be performed.

At step 3030, the processing unit may use the MPM indicator to determine an intra prediction mode for the target block.

The processing unit may obtain the MPM indicator from the bitstream.

The processing unit may determine the MPM indicated by the MPM indicator among the one or more MPMs in the MPM list as the intra prediction mode of the target block.

For example, the MPM indicator may be an index to the MPM list.

At step 3040, the processing unit may derive one or more possible remaining modes for the target block.

The processing unit may derive one or more possible remaining modes in the list of possible remaining modes for the target block.

At step 3050, the processing unit may use the remaining mode indicator to determine an intra-prediction mode for the target block.

The processing unit may obtain the remaining mode indicator from the bitstream.

The processing unit may determine the possible remaining mode indicated by the remaining mode indicator among the one or more possible remaining modes in the list of possible remaining modes as the intra prediction mode of the target block.

For example, the remaining mode indicator may be an index into a list of possible remaining modes.

As described above, the intra prediction mode of the target block may be determined based on a number of different lists corresponding to the MPM list and the list of possible remaining modes.

31 illustrates derivation of MPM after determining whether to use MPM and determination of intra prediction mode using residual mode, according to an embodiment.

The order of steps 3010 and 3020 described above with reference to FIG. 30 may be changed.

At step 3110, the processing unit may determine whether MPM is used to perform intra prediction for the target block.

Here, the fact that the MPM is used to perform intra prediction for the target block may represent: 1) the case where the intra prediction mode of the target block is one of the MPMs, and 2) the intra prediction mode of the target block is the residual mode one of and the MPM list is used for the remaining modes.

The processing unit may use the MPM usage indicator to determine whether MPM is used to perform intra prediction for the target block. The processing unit may obtain the MPM usage indicator from the bitstream.

For example, the MPM usage indicator may have a name such as "prev_intra_pred_mode flag".

When the value of the MPM usage indicator is a first value (eg, "1"), the processing unit may determine that MPM is used to perform intra prediction for the target block.

When the value of the MPM usage indicator is a second value (eg, "0"), the processing unit may determine that MPM is not used to perform intra prediction for the target block.

The processing unit may use the MPM indicator to determine whether MPM is used to perform intra prediction for the target block. If it is determined that the MPM indicator indicates one of MPM and possible remaining modes, the processing unit may determine that MPM is used to perform intra prediction for the target block. If it is determined that the MPM indicator does not indicate one of MPM and possible remaining modes, the processing unit may determine that MPM is not used to perform intra prediction for the target block.

If it is determined that MPM is used to perform intra prediction for the target block, step 3120 may be performed.

If it is determined that MPM is not used to perform intra prediction of the target block, the process may be terminated and intra prediction based on the additional scheme may be performed.

At step 3120, the processing unit may derive one or more MPMs for the target block.

The processing unit may derive one or more MPMs in the list of MPMs for the target block.

At step 3130, the processing unit may determine whether the possible remaining mode is used to perform intra prediction for the target block.

Alternatively, the processing unit may determine which of the MPM and possible remaining modes is used to perform intra prediction for the target block.

In an example, if it is determined that the MPM indicator indicates one of the possible remaining modes, the processing unit may determine that the possible remaining modes are used to perform intra prediction for the target block.

In an example, if it is determined that the MPM indicator does not indicate one of the possible remaining modes, the processing unit may determine that the possible remaining modes are not used to perform intra prediction for the target block.

In an example, if it is determined that the MPM indicator indicates one of the MPMs, the processing unit may determine that the MPM is used to perform intra prediction for the target block.

In an example, if it is determined that the possible remaining mode is used to perform intra prediction for the target block, step 3150 may be performed.

In an example, if it is determined that MPM is used to perform intra prediction for the target block, step 3140 may be performed.

In an example, if it is determined that the intra prediction mode of the target block is one of MPM, step 3140 may be performed.

In an example, if it is determined that the intra prediction mode of the target block is one of the possible remaining modes, step 3150 may be performed.

Step 3140 may correspond to step 3030 . Duplicate description will be omitted here

Step 3150 may correspond to step 3040 . Duplicate description will be omitted here

The possible remaining modes may be derived based on the MPM derived at step 3120. The relationship between the MPM and the possible remaining modes and the derivation of the possible remaining modes under the relationship will be described in detail below.

Step 3160 may correspond to step 3050. Duplicate description will be omitted here

Steps 3040 and 3150 can be optionally performed. In an example, the processing unit may use the remaining mode usage indicator to determine whether the intra prediction mode of the target block is one of the possible remaining modes. The processing unit may obtain the remaining mode usage indicator from the bitstream. When the value of the remaining mode usage indicator is a first value (eg, "1"), the processing unit may determine that the intra prediction mode of the target block is one of the possible remaining modes. When the value of the remaining mode usage indicator is a second value (eg, "0"), the processing unit may determine that the intra prediction mode of the target block is not one of the possible remaining modes. If it is determined that the intra prediction mode of the target block is one of the possible remaining modes, step 3040 or 3150 may be performed. If it is determined that the intra prediction mode of the target block is not one of the possible remaining modes, the process may be terminated, and additional intra prediction using neither MPM nor the possible remaining modes may be processed.

Derivation of possible residual modes

Figure 32 shows blocks for deriving MPM candidates, according to an example.

The processing unit may derive one or more of the remaining intra-prediction modes other than MPM among all intra-prediction modes as possible remaining modes.

The number of possible remaining modes can be predefined. For example, the number of possible remaining modes may be 2 or 3.

For example, assuming that the total number of intra prediction modes is 67 and the number of MPMs is 6, the number of possible remaining modes may be 2.

For example, assuming that the total number of intra prediction modes is 67 and the number of MPMs is 6, the number of possible remaining modes may be 3.

The six MPM candidates (ie, candModeList[0] to candModeList[5]) may be derived as described below.

1) When the intra prediction mode candIntraPredModeA of the adjacent block A of the target block and the intra prediction mode candIntraPredModeB of the adjacent block B of the target block are the same as each other, and the intra prediction mode candIntraPredModeA of the adjacent block A is greater than INTRA_DC, the following code 1 The six MPM candidates are derived as shown in .

[Code 1]

candModeList[0] = Intra prediction mode of adjacent block A (candIntraPredModeA)

candModeList[1]=INTRA_PLANAR

candModeList[2]=INTRA_DC

candModeList[3]=2+((candIntraPredModeA+61)%64)

candModeList[4]=2+((candIntraPredModeA-1)%64)

candModeList[5]=2+((candIntraPredModeA+60)%64)

2) When the above conditions in 1) are not satisfied (that is, when the intra prediction mode candIntraPredModeA of the adjacent block A and the intra prediction mode candIntraPredModeB of the adjacent block B are different from each other and the intra prediction mode of the adjacent block A candIntraPredModeA or adjacent When the intra prediction mode of block B candIntraPredModeB is greater than INTRA_DC), MPM candidates can be derived as shown in the following code 2 to code 7:

[Code 2]

minAB=candModeList[(candModeList[0]>candModeList[1])? 1:0]

maxAB=candModeList[(candModeList[0]>candModeList[1])? 0:1]

2-1) When both the intra prediction mode candIntraPredModeA of the adjacent block A and the intra prediction mode candIntraPredModeB of the adjacent block B are greater than INTRA_DC, the MPM candidate can be derived as shown in the following code 3:

[Code 3]

candModeList[0]=candIntraPredModeA

candModeList[1]=candIntraPredModeB

candModeList[2]=INTRA_PLANAR

candModeList[3]=INTRA_DC

When the difference between the derived MaxAB and MinAB falls within the range from 2 to 62, the fifth and sixth MPM candidates can be derived as shown in Code 4 below:

[Code 4]

candModeList[4]=2+((maxAB+61)%64)

candModeList[5]=2+((maxAB-1)%64)

When the difference between the derived MaxAB and MinAB does not fall within the range from 2 to 62, the fifth and sixth MPM candidates can be derived as shown in Code 5 below:

[Code 5]

candModeList[4]=2+((maxAB+60)%64)

candModeList[5]=2+((maxAB)%64)

2-2) When the condition in 2-1) is not satisfied (that is, when at least one of the intra prediction mode candIntraPredModeA of the adjacent block A and the intra prediction mode candIntraPredModeB of the adjacent block B is greater than INTRA_DC), it may be as follows Six MPM candidates are derived as shown in Listing 6:

[Code 6]

candModeList[0]=candIntraPredModeA

candModeList[1]=candIntraPredModeB

candModeList[2]=1-minAB

candModeList[3]=2+((maxAB+61)%64)

candModeList[4]=2+((maxAB-1)%64)

candModeList[5]=2+((maxAB+60)%64)

3) When the above conditions in 1) and 2) are not satisfied, six MPM candidates can be derived as shown in the following code 7:

[Code 7]

candModeList[0]=candIntraPredModeA

candModeList[1]=(candModeList[0]==INTRA_PLANAR)? INTRA_DC:INTRA_PLANAR

candModeList[2]=INTRA_ANGULAR50

candModeList[3]=INTRA_ANGULAR18

candModeList[4]=INTRA_ANGULAR46

candModeList[5]=INTRA_ANGULAR54

The processing unit may derive possible remaining modes based on spatially and temporally neighboring blocks of the target block.

The processing unit may derive at least one intra prediction mode not belonging to the MPM among the intra prediction modes of the spatially adjacent blocks of the target block and the intra prediction modes of the temporally adjacent blocks of the target block as possible remaining modes.

For example, when the number of the intra prediction mode of one of the adjacent blocks of the target block is 30 and the number of the other intra prediction mode is 40, and when the intra prediction mode No. 30 belongs to MPM and the intra prediction mode No. 40 When the prediction mode does not belong to the MPM, the intra prediction mode No. 40 may be derived as a possible remaining mode.

The processing unit may derive possible remaining modes based on the MPM selected from all MPMs.

The selected MPM may be a predefined number of MPMs preceding in order. Here, the preceding MPM may represent an intra prediction mode defined by a smaller number of bins. Alternatively, the first MPM in order may be the MPM with the lowest index in the MPM list.

In an embodiment, the predefined number of selected MPMs may be "1".

The derived number of possible remaining modes may be the sum of the number of the first MPM and the offset. For example, when the number of the first MPM is 30, the sum of the number "30" and the offset "1" is 31, and thus the intra prediction mode No. 31 can be derived as a possible remaining mode.

The derived number of possible remaining modes may be the difference between the number of the first MPM and the offset. For example, when the number of the first MPM is 30, the difference between the number "30" and the offset "1" is 29, and thus the No. 29 intra prediction mode can be derived as a possible remaining mode.

The derived number of possible remaining modes may be: 1) the sum of the number and offset of the first MPM, and 2) the difference between the number and offset of the first MPM. In an example, when the number of the first MPM is 30, the intra prediction mode No. 29 and the intra prediction mode No. 31 may be derived as possible remaining modes.

The derived number of possible remaining modes may be: 1) the sum of the number of the first MPM and the first offset, and 2) the difference between the number of the first MPM and the first offset. For example, the first offset may be one.

When 1) an intra prediction mode with a number corresponding to the sum of the number of the first MPM and the first offset or 2) an intra prediction mode with a number corresponding to the difference between the number of the first MPM and the first offset When the prediction mode is one of the existing MPMs, 1) an intra prediction mode with a number corresponding to the sum of the number of the first MPM and the second offset, or 2) an intra prediction mode with a number corresponding to the number of the first MPM and the second offset. The numbered intra prediction mode corresponding to the difference between the shifts may be derived as possible remaining modes. For example, the second offset may be 2. Optionally, the second offset may be different from the first offset. Alternatively, the second offset may be a value obtained by adding "1" to the first offset or by adding a predefined number to the first offset.

For example, when the intra prediction mode having the number corresponding to the sum of the number of the first MPM and the first offset is one of the existing MPMs, the intra prediction mode having the number corresponding to the sum of the number of the first MPM and the second offset The numbered intra prediction modes of can be derived as possible remaining modes.

For example, when the intra prediction mode having the number corresponding to the difference between the number of the first MPM and the first offset is one of the existing MPMs, the intra prediction mode having the number corresponding to the difference between the number of the first MPM and the second offset The numbered intra prediction modes corresponding to the difference between can be derived as possible remaining modes.

In an embodiment, the predefined number of selected MPMs may be '3'.

For example, the processing unit may add the offset to the number of the first MPM, the second MPM and the third MPM among the one or more MPMs in the MPM list or by adding the offset from the first MPM, the second MPM and the third MPM The offset is subtracted from the number of the three MPMs to determine the number of possible remaining modes.

For example, when the numbers of the first MPM, the second MPM, and the third MPM are 30, 40, and 50, respectively, the numbers of possible remaining modes that are derived may be 31, 41, and 51, respectively.

When the particular mode is not included in the MPM, the processing unit may derive the particular mode as possible remaining modes. For example, the specific mode may be a non-directional mode. The non-directional mode may be a DC mode and/or a planar mode.

For example, when the DC mode is not included in the MPM, the DC mode may become the first possible residual mode or the second possible residual mode.

For example, when the planar mode is not included in the MPM, the planar mode may be the first possible residual mode or the second possible residual mode.

The processing unit may derive possible remaining modes based on the direction of the MPM.

For example, the processing unit may derive an intra-prediction mode for a specified direction as a possible remaining mode based on the direction of the MPM.

For example, the processing unit may derive an intra-prediction mode having a direction that does not belong to the direction of the MPM in the specified direction as a possible remaining mode based on the direction of the MPM.

For example, when all MPMs are intra prediction modes with horizontal directionality, intra prediction modes with vertical directionality may be derived as possible remaining modes. The intra prediction mode with horizontal directionality may be an intra prediction mode having a slope in which the change of the horizontal component is larger than that of the vertical component. The intra prediction mode having vertical directivity may be an intra prediction mode having a slope in which the change of the vertical component is larger than that of the horizontal component.

For example, when all MPMs are intra prediction modes with vertical directionality, intra prediction modes with horizontal directionality or horizontal intra prediction modes may be derived as possible remaining modes.

For example, when all MPMs are intra prediction modes with horizontal directionality, intra prediction modes with vertical directionality or vertical intra prediction modes may be derived as possible remaining modes.

The processing unit may derive possible remaining modes based on the statistics of the selected MPM. The selected MPM may be a predefined number of MPMs preceding in order.

In other words, the intra prediction mode with the number corresponding to the statistic value can be derived as the possible remaining mode.

For example, the intra prediction mode numbered as the average of the number of the first MPM and the number of the second MPM may be derived as the possible remaining modes. When the number of the first MPM is 30 and the number of the second MPM is 40, the intra prediction mode No. 35 may be derived as a possible remaining mode.

When deriving possible remaining modes based on the statistics of the selected MPM, the processing unit may exclude the DC mode and the planar mode as non-directional modes. Optionally, when selecting a pre-defined number of MPMs in sequence from all MPMs, the processing unit may not select an MPM that is a non-directional mode among the pre-defined number of MPMs in sequence. The corresponding MPM for the directional mode, and the subsequent MPM for the directional mode can be selected.

For example, the processing unit may calculate an average of the first two MPMs in order out of a total of six MPMs, and may derive an intra-prediction mode with a number corresponding to the average as a possible remaining mode. When the six MPMs respectively indicate the DC mode, the 30th mode, the plane mode, the 10th mode, the 50th mode and the 52nd mode, the MPM as the DC mode and the MPM as the plane mode may be excluded from selection. MPM No. 30 and MPM No. 10, which are the first two MPMs in order, can be selected due to such exclusion, and the average value of 30 and 10 is 20, so the intra prediction mode No. 20 can be derived as possible remaining modes.

The processing unit may derive possible remaining modes based on the statistics of all MPMs. The number of intra prediction modes derived as possible remaining modes may be this statistic. For example, the total number of MPMs may be 6, and the statistic may be its average.

When deriving possible remaining modes based on the statistics of the selected MPM, the processing unit may exclude the DC mode and the planar mode as non-directional modes.

For example, the processing unit may exclude DC mode and planar mode from all MPMs, and may derive possible remaining modes based on statistics of the remaining MPMs. Intra prediction modes with numbers corresponding to the statistic can be derived as possible remaining modes.

The processing unit may use the list of possible remaining mode candidates to derive the possible remaining modes.

The list of possible remaining mode candidates may include one or more possible remaining mode candidates. The list of possible remaining mode candidates may be equally defined by the encoding apparatus 1600 and the decoding apparatus 1700 .

The processing unit may sequentially search for possible remaining mode candidates present in the list of possible remaining mode candidates, and may derive possible remaining mode candidates that do not belong to the MPM as possible remaining modes.

Searching for possible remaining mode candidates sequentially may mean that possible remaining mode candidates with smaller indexes in the list of possible remaining mode candidates are searched earlier than possible remaining mode candidates with larger indexes.

The number of possible remaining mode candidates derived as possible remaining modes among the possible remaining mode candidates in the possible remaining mode candidate list may be predefined.

For example, when the possible remaining mode candidates are selected in the order of intra prediction mode No. 30, intra prediction mode No. 40, intra prediction mode No. 50, intra prediction mode No. 20, and intra prediction mode No. 10 defined, and intra prediction mode No. 30 and intra prediction mode No. 40 belong to MPM, if the number of possible residual mode candidates that are derived as possible residual modes is 1, then intra prediction mode No. 50 can be derived for possible remaining modes.

Optionally, as described above, when possible remaining mode candidates are defined, and intra prediction mode No. 30 and intra prediction mode No. 40 belong to MPM, if the number of possible remaining mode candidates that are derived as possible remaining modes is 3, then the intra prediction mode No. 50, the intra prediction mode No. 20 and the intra prediction mode No. 10 can be derived as the first possible residual mode, the second possible residual mode and the third possible residual mode, respectively.

The processing unit may derive at least one intra-prediction mode as a possible remaining mode based on the number of intra-prediction modes in the remaining mode candidates.

In an example, among 61 remaining mode candidates obtained by excluding six MPM candidate modes from a total of 67 intra-prediction modes, the first possible remaining mode may be derived individually from the mode with the smallest intra-prediction mode number in ascending order mode, the second possible remaining mode and the third possible remaining mode. In an example, where the number of intra prediction modes is 67 and the number of MPMs is 6 (ie, 20, 30, 0, 1, 31, 32), the first remaining mode may be defined as the remaining mode (2 , 3, 4, . . . , 19, 21, 22, . . , 29, 33, 34, . 3, 4).

In an example, among 61 remaining mode candidates obtained by excluding six MPM candidate modes from a total of 67 intra-prediction modes, the first possible remaining mode may be derived individually from the mode with the largest intra-prediction mode number in descending order , the second possible residual mode and the third possible residual mode.

Use the remaining mode indicator to determine the intra prediction mode

33 illustrates binarization of residual mode indicators according to an example.

In FIG. 33, the sign and truncated binary code of the remaining mode indicator are depicted, and the remaining mode indicated by the sign and the truncated binary code is depicted.

The processing unit may use the remaining mode indicator to determine the intra-prediction mode of the target block.

The intra prediction mode indicated by the remaining mode indicator may include both a possible remaining mode and a pure remaining mode. In other words, the residual mode indicator may indicate one of the possible residual mode and the pure residual mode as the intra prediction mode of the target block.

The remaining mode indicator may be a value binarized using a truncated binary encoding method.

As shown in FIG. 33, the number of bins in the possible residual mode and the number of bins in the pure residual mode may be different from each other.

For example, the number of possible remaining modes may be two.

For example, assuming that the total number of intra prediction modes is 67 and the number of MPMs is 6, the number of possible remaining modes may be 2 and the number of pure remaining modes may be 59. In other words, intra prediction modes that do not belong to MPM among all intra prediction modes can be classified into two possible residual modes and 59 pure residual modes.

The possible residual mode may have five bins, and the pure residual mode may have six bins.

In an embodiment, the bins for the two possible remaining modes may be defined as "00000" and "00001". "00000" may indicate the first possible remaining mode. "00001" may indicate the second possible remaining mode.

The bins for the 59 pure residual modes may be defined as six bins other than "000000", "000001", "000010" and "000011". For example, the bins for pure residual mode may include "000100", "000101", etc.

As described above, the processing unit may use the binarized values to encode and/or decode the remaining mode indicators.

In another embodiment, the bins for the two possible remaining modes may be defined as "11110" and "11111". "11110" may indicate the first possible remaining mode. "11111" may indicate the second possible remaining mode.

The bins for the 59 pure residual modes may be defined as six bins other than "111100", "111101", "111110" and "111111". For example, the bins for pure residual mode may include "111000", "111001", etc.

As described above, the processing unit may use the binarized values to encode and/or decode the remaining mode indicators.

When the total number of intra prediction modes is 67 and the number of MPMs is 6, the number of possible remaining modes may be 3 and the number of pure remaining modes may be 58. In other words, intra prediction modes that do not belong to MPM among all intra prediction modes can be classified into three possible residual modes and 58 pure residual modes.

The possible residual mode may have five bins, and the pure residual mode may have six bins.

In an embodiment, the bins for the three possible remaining modes may be defined as "00000", "00001" and "00010". "00000" may indicate the first possible remaining mode. "00001" may indicate the second possible remaining mode. "00010" may indicate the third possible remaining mode.

The bins for the 58 pure residual modes can be defined as the sum of the binarization value and offset 3. For example, the bins for pure residual mode may include "000110" (="000011" + "000011"), "000111" (="000100" + "000011"), "001000", "001001", and the like.

As described above, the processing unit may use the binarized values to encode and/or decode the remaining mode indicators.

FIG. 34 is a flowchart of a target block prediction method and a bitstream generation method according to an embodiment.

The target block prediction method and the bitstream generation method according to the present embodiment may be performed by the encoding apparatus 1600 . This embodiment may be part of a target block coding method or a video coding method.

At step 3410, processing unit 1610 may determine an intra-prediction mode to be applied to the encoding of the target block.

Step 3410 may correspond to step 1810 described above with reference to FIG. 18 . Also, step 3410 may correspond to step 3010 , step 3020 , step 3030 , step 3040 , and step 3050 described above with reference to FIG. 30 . Also, step 3410 may correspond to step 3110 , step 3120 , step 3130 , step 3140 , and step 3150 described above with reference to FIG. 31 .

The determined intra prediction mode may be 1) a bidirectional intra prediction mode and/or 2) an intra prediction mode using the remaining modes.

Intra prediction may be 1) bidirectional intra prediction and/or 2) intra prediction using residual mode.

Among the intra-prediction modes available for the target block, the processing unit 1610 may determine the intra-prediction mode for the target block considering the rate-distortion cost of the intra-prediction mode.

In step 3420, the processing unit 1610 may perform intra prediction for the target block using the determined intra prediction mode.

Step 3420 may correspond to step 1820 described above with reference to FIG. 18 .

The information on the encoded target block may be generated by performing intra prediction on the target block using an intra prediction mode.

The prediction block may be generated through intra prediction of the target block using the intra prediction mode, and a residual block which is a difference between the target block and the prediction block may be generated. Information about the encoded target block may be generated by applying transform and quantization to the residual block.

The information about the encoded target block may include transform and quantization coefficients of the target block. The information about the encoded target block may include encoding parameters of the target block.

At step 3430, the processing unit 1610 may generate a bitstream.

The bitstream may include information about the encoded target block.

The bitstream may include prediction information. The prediction information may be information for bidirectional intra prediction and/or intra prediction using residual mode. In other words, the prediction information may include coding parameters related to the target block required for intra prediction as described in the embodiments.

For example, prediction information may include 1) unidirectional/bidirectional classification indicator, 2) intra prediction mode indicator, 3) weight for reference pixels, 4) MPM usage indicator, 5) MPM for bidirectional intra prediction indicator, 6) predefined angle α, etc.

For example, the prediction information may include 1) MPM usage indicator, 2) MPM indicator, 3) remaining mode indicator, 4) remaining mode usage indicator, etc. for intra prediction using remaining mode.

Predictive information may be generated at step 3430 , or may be generated, at least in part, at steps 3410 and 3420 .

The processing unit 1610 may store the generated bitstream in the memory 1640 . Alternatively, the communication unit 1620 may transmit the bitstream to the decoding apparatus 1700 .

The processing unit 1610 may perform entropy encoding on the prediction information, and may generate a bitstream including the entropy-encoded prediction information.

The embodiments may be combined with the operations of the encoding apparatus 100 described above with reference to FIG. 1 . For example, the operations at step 3410 and step 3420 may be performed by intra prediction unit 120 . The operations at step 3430 may be performed by the entropy encoding unit 150 . Furthermore, operations performed by other components of the encoding device 100 may be performed before, after, and while steps 3410, 3420, and 3430 are performed.

FIG. 35 is a flowchart of a target block prediction method using a bitstream according to an embodiment.

The target block prediction method using the bitstream according to the present embodiment may be performed by the decoding apparatus 1700 . The embodiments may be part of a target block decoding method or a video decoding method.

At step 3510, the communication unit 1720 may obtain the bitstream. The communication unit 1720 may receive the bitstream from the encoding apparatus 1600 .

The bitstream may include information about the encoded target block.

The information about the encoded target block may include transform and quantization coefficients of the target block. The information about the encoded target block may include encoding parameters of the target block.

The bitstream may include prediction information. The prediction information may be information for bidirectional intra prediction and/or intra prediction using residual mode. In other words, the prediction information may include coding parameters related to the target block required for intra prediction as described in the embodiments.

For example, prediction information may include 1) unidirectional/bidirectional classification indicator, 2) intra prediction mode indicator, 3) weight for reference pixels, 4) MPM usage indicator, 5) MPM for bidirectional intra prediction indicator, 6) predefined angle α, etc.

For example, the prediction information may include 1) MPM usage indicator, 2) MPM indicator, 3) remaining mode indicator, 4) remaining mode usage indicator, etc. for intra prediction using remaining mode.

The processing unit 1710 may store the acquired bitstream in the memory 1740 .

The processing unit 1710 may obtain prediction information from the bitstream. The processing unit 1710 may obtain prediction information by performing entropy decoding on the entropy-encoded prediction information of the bitstream.

At step 3520, processing unit 1710 may determine an intra-prediction mode to be applied to decoding of the target block.

Step 3520 may correspond to step 1810 described above with reference to FIG. 18 . Also, step 3520 may correspond to step 3010 , step 3020 , step 3030 , step 3040 , and step 3050 described above with reference to FIG. 30 . Further, step 3520 may correspond to step 3110, step 3120, step 3130, step 3140, and step 3150 described above with reference to FIG. 31 .

The determined intra prediction mode may be 1) a bidirectional intra prediction mode and/or 2) an intra prediction mode using the remaining modes.

Intra prediction may be 1) bidirectional intra prediction and/or 2) intra prediction using residual mode.

The processing unit 1710 may determine an intra prediction mode of the target block based on the prediction information.

At step 3530, the processing unit 1710 may perform intra prediction for the target block using the information about the encoded target block and the determined intra prediction mode.

Step 3530 may correspond to step 1820 described above with reference to FIG. 18 . Also, in step 3530, a prediction block may be generated by performing intra prediction on the target block using the intra prediction mode, and a reconstructed block which is the sum of the prediction block and the reconstructed residual block may be generated.

The embodiments may be combined with the operations of the decoding apparatus 200 described above with reference to FIG. 2 . For example, the operations at step 3510 may be performed by entropy decoding unit 210. The operations at steps 3520 and 3530 may be performed by the intra prediction unit 240 . Furthermore, operations performed by other components of the decoding apparatus 200 may be performed before, after, and while steps 3510, 3520, and 3530 are performed.

In the above-described embodiments, although the method has been described based on the flowchart as a series of steps or units, the present disclosure is not limited to the order of the steps, and some steps may be in a different order than the described order of steps to be performed or concurrently with other steps. Furthermore, those skilled in the art will understand that the steps shown in the flowcharts are not exclusive and may include other steps, or that one or more of the flowcharts may be deleted without departing from the scope of the present disclosure steps.

The above-described embodiments according to the present disclosure can be implemented as programs that can be executed by various computer devices, and can be recorded on a computer-readable storage medium. Computer-readable storage media may include program instructions, data files, and data structures, alone or in combination. The program instructions recorded on the storage medium may be specially designed or configured for the present disclosure, or may be known or available to those of ordinary skill in the computer software arts.

Computer-readable storage media may include information used in embodiments of the present disclosure. For example, a computer-readable storage medium may include a bitstream, and the bitstream may contain the information described above in the embodiments of the present invention.

Computer-readable storage media may include non-transitory computer-readable media.

Examples of computer-readable storage media may include all types of hardware devices specially configured to record and execute program instructions, such as magnetic media (such as hard disks, floppy disks, and magnetic tapes), optical media (such as compact disk (CD)-ROMs) and Digital Versatile Disc (DVD)), magneto-optical media such as floppy disk, ROM, RAM and flash memory. Examples of program instructions include machine code, such as code created by a compiler, and high-level language code that can be executed by a computer using an interpreter. A hardware device may be configured to operate as one or more software modules to perform the operations of the present disclosure, and vice versa.

As described above, although the present disclosure has been described based on specific details, such as detailed components and a limited number of embodiments and drawings, the specific details are provided only to facilitate understanding of the present disclosure and the present disclosure is not limited to these embodiments , those skilled in the art will practice various changes and modifications based on the above description.

Therefore, it should be understood that the spirit of the present embodiment is not limited to the above-described embodiment and that the appended claims and their equivalents and modifications thereto fall within the scope of the present disclosure.

Claims (20)

1. A decoding method, comprising:

determining a decoded intra prediction mode to be applied to the target block; and is

Performing intra prediction for a target block using the determined intra prediction mode,

wherein the intra prediction mode is a bi-directional intra prediction mode, and

wherein the intra prediction is bi-directional intra prediction.

2. The decoding method of claim 1, wherein the bidirectional intra prediction mode is determined based on availability of pixels in a neighboring block located in a specified direction of a target block.

3. The decoding method of claim 1, wherein the bidirectional intra prediction mode is determined based on prediction modes of neighboring blocks of a target block.

4. The decoding method of claim 1, wherein the two directions of the bi-directional intra prediction are two opposite linear directions.

5. The decoding method of claim 1, wherein:

generating virtual neighboring pixels in a specified direction of a target block and performing the bidirectional intra prediction for the target block using the virtual neighboring pixels, and

the specified direction is one or more of a right direction and a down direction.

6. The decoding method of claim 1, wherein a prediction value for a target pixel in a target block is derived using pixels in neighboring blocks located in both directions of the bi-directional intra prediction.

7. The decoding method of claim 1, wherein a prediction value for a target pixel is derived using weights according to distances between respective pixels located in neighboring blocks in both directions of the bi-directional intra prediction and the target pixel in the target block.

8. The decoding method of claim 1, wherein weights for two directions of the bi-directional intra prediction are used to derive a prediction value for a target pixel in a target block.

9. The decoding method of claim 1, wherein a unidirectional/bidirectional classification indicator and an intra prediction mode indicator are used to determine whether the bidirectional intra prediction mode for a target block is to be used.

10. The decoding method of claim 1, wherein the two directions of the bi-directional intra prediction are determined based on two directions indicated by two intra prediction mode indicators.

11. The decoding method of claim 1, wherein a single intra prediction mode indicator indicates one of a direction of unidirectional intra prediction and a direction of the bidirectional intra prediction.

12. The decoding method of claim 1, wherein one of the unidirectional intra prediction and the bidirectional intra prediction is selected according to availability of reference pixels in a direction corresponding to a direction indicated by an intra prediction mode indicator.

13. The decoding method of claim 1, wherein it is determined which one of unidirectional intra prediction and the bidirectional intra prediction is to be used for the entire target block.

14. The decoding method of claim 1, wherein it is determined which one of unidirectional intra prediction and the bidirectional intra prediction is to be used for each of the pixels in the target block.

15. The decoding method of claim 1, wherein for the first direction and the second direction of the bi-directional intra prediction, when a reference pixel in the first direction or a reference pixel in the second direction is unavailable, a value of the unavailable reference pixel is generated using padding.

16. The decoding method of claim 1, wherein:

determining a prediction value for a target pixel in a target block using at least one of reference pixels located in two prediction directions of the bi-directional intra prediction mode, and

applying a weight to each of the reference pixels.

17. The decoding method of claim 1, wherein:

the residual mode indicator indicates a residual mode to be used for intra prediction of the target block among the plurality of residual modes, and

the plurality of remaining modes are remaining intra prediction modes other than MPMs existing in a most probable mode MPM list.

18. The decoding method of claim 1, wherein the intra prediction mode is determined based on a plurality of different lists.

19. An encoding method, comprising:

determining a decoded intra prediction mode to be applied to the target block; and is

Performing intra prediction for a target block using the determined intra prediction mode,

wherein the intra prediction mode is a bi-directional intra prediction mode, and

wherein the intra prediction is bi-directional intra prediction.

20. A computer-readable storage medium storing a bitstream for image decoding, the bitstream comprising:

Information on the target block that is encoded,

wherein an intra prediction mode to be applied to decoding of the target block is determined, and

wherein the intra prediction for the target block using the information on the encoded target block and the determined intra prediction mode is performed.

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